Lipid Synthesis Enzymes Research Articles

Adiponectin Enhances Human Keratinocyte Lipid Synthesis via SIRT1 and Nuclear Hormone Receptor Signaling

Adiponectin is known to have beneficial effects on lipid and insulin metabolism, wound healing, and cellular senescence, but its effect on skin barrier formation remains unknown. We investigated the effects of adiponectin on keratinocyte lipid synthesis with respect to skin barrier function. Lipid staining revealed an adiponectin-mediated increase in keratinocyte intracellular and reconstructed epidermal lipid content. Moreover, significant increases in the levels of ceramide and its downstream metabolites (sphingosine and sphingosine-1-phosphate) following adiponectin stimulation were detected using liquid chromatography-mass spectrometry. Expression levels of keratinocyte differentiation markers were also increased. Adiponectin also increased expression of lipid biosynthesis enzymes (fatty acid synthase, HMG-CoA reductase, and serine palmitoyltransferase), nuclear hormone receptors (peroxisome proliferator-activated receptors and liver X receptors), and the adiponectin signal molecule SIRT1. Suppression of SIRT1, liver X receptor-α, or peroxisome proliferator-activated receptor-α downregulated the expression of lipid synthetic enzymes, decreasing lipid content. Inhibition of adiponectin receptors decreased expression of nuclear hormone receptors, SIRT1, lipid-synthesizing enzymes, and sphingolipids. Thus, activation of adiponectin signaling increases the expression of transcription factors, including SIRT1, liver X receptor-α, and peroxisome proliferator-activated receptor-α, enhancing lipid synthesis and keratinocyte cell differentiation and possibly aiding in the maintenance of skin barrier homeostasis.

Lipid Synthesis Is Required to Resolve Endoplasmic Reticulum Stress and Limit Fibrotic Responses in the Lung.

Endoplasmic reticulum (ER) stress is evident in the alveolar epithelium of humans and mice with pulmonary fibrosis, but neither the mechanisms causing ER stress nor the contribution of ER stress to fibrosis is understood. A well-recognized adaptive response to ER stress is that affected cells induce lipid synthesis; however, we recently reported that lipid synthesis was downregulated in the alveolar epithelium in pulmonary fibrosis. In the present study, we sought to determine whether lipid synthesis is needed to resolve ER stress and limit fibrotic remodeling in the lung. Pharmacologic and genetic manipulations were performed to assess whether lipid production is required for resolving ER stress and limiting fibrotic responses in cultured alveolar epithelial cells and whole-lung tissues. Concentrations of ER stress markers and lipid synthesis enzymes were also measured in control and idiopathic pulmonary fibrosis lung tissues. We found that chemical agents that induce ER stress (tunicamycin or thapsigargin) enhanced lipid production in cultured alveolar epithelial cells and in the mouse lung. Moreover, lipid production was found to be dependent on the enzyme stearoyl-coenzyme A desaturase 1, and when pharmacologically inhibited, ER stress persisted and lung fibrosis ensued. Conversely, lipid production was reduced in mouse and human fibrotic lung, despite there being an increase in the magnitude of ER stress. Furthermore, augmenting lipid production effectively reduced ER stress and mitigated fibrotic remodeling in the mouse lung after exposure to silica. Augmenting lipid production reduces ER stress and attenuates fibrotic remodeling in the mouse lung, suggesting that similar approaches might be effective for treating human fibrotic lung diseases.

Tissue-selective alteration of ethanolamine plasmalogen metabolism in dedifferentiated colon mucosa

Human colon lipid analysis by imaging mass spectrometry (IMS) demonstrates that the lipid fingerprint is highly sensitive to a cell's pathophysiological state. Along the colon crypt axis, and concomitant to the differentiation process, certain lipid species tightly linked to signaling (phosphatidylinositols and arachidonic acid (AA)-containing diacylglycerophospholipids), change following a rather simple mathematical expression. We extend here our observations to ethanolamine plasmalogens (PlsEtn), a unique type of glycerophospholipid presenting a vinyl ether linkage at sn-1 position. PlsEtn distribution was studied in healthy, adenomatous, and carcinomatous colon mucosa sections by IMS. In epithelium, 75% of PlsEtn changed in a highly regular manner along the crypt axis, in clear contrast with diacyl species (67% of which remained constant). Consistently, AA-containing PlsEtn species were more abundant at the base, where stem cells reside, and decreased while ascending the crypt. In turn, mono−/diunsaturated species experienced the opposite change. These gradients were accompanied by a gradual expression of ether lipid synthesis enzymes. In lamina propria, 90% of stromal PlsEtn remained unchanged despite the high content of AA and the gradient in AA-containing diacylglycerophospholipids. Finally, both lipid and protein gradients were severely affected in polyps and carcinoma. These results link PlsEtn species regulation to cell differentiation for the first time and confirm that diacyl and ether species are differently regulated. Furthermore, they reaffirm the observations on cell lipid fingerprint image sensitivity to predict cell pathophysiological status, reinforcing the translational impact both lipidome and IMS might have in clinical research.

MP70-14 REGULATION OF PROSTATE CANCER METABOLISM AND INVASIVENESS BY THE LIVER X RECEPTOR

You have accessJournal of UrologyProstate Cancer: Basic Research & Pathophysiology III1 Apr 2018MP70-14 REGULATION OF PROSTATE CANCER METABOLISM AND INVASIVENESS BY THE LIVER X RECEPTOR Allison May, Suomia Abuirqeba, Zachary Hamilton, Colin Flaveny, and Sameer Siddiqui Allison MayAllison May More articles by this author , Suomia AbuirqebaSuomia Abuirqeba More articles by this author , Zachary HamiltonZachary Hamilton More articles by this author , Colin FlavenyColin Flaveny More articles by this author , and Sameer SiddiquiSameer Siddiqui More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2018.02.2258AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Prostate cancer (PCa) progression is marked by characteristic changes in PCa cell metabolism. During early PCa cell transformation, activation of the oncogene, c-MYC, fosters a metabolic switch from glycolytic to oxidative metabolism and increases lipid synthesis. This switch in metabolic activity and increased expression of lipid synthesis genes is characteristic of castration resistant metastatic PCa. The liver X receptor (LXR) is a transcriptional regulator expressed in prostate epithelial cells that plays an important role in cholesterol, lipogenic and carbohydrate homeostasis. Recently, it has been demonstrated that loss of the bona-fide PCa tumor-suppressor, PTEN, results in oncogene driven dysregulation of LXR-target gene expression. Therefore, we theorized that LXRs may play a role in directing PCa metabolism and treatment resistance. METHODS First, we assessed DNA and RNA sequencing data from prostate tumor samples to determine if lipid synthesis enzyme expression correlated with LXR expression in tumors. Second, we compared the expression of LXRs and LXR target genes in culture PCa cells that display differential dependence on androgens for growth. Third, we tested whether disruption of LXR transcriptional activity using pharmacological and genetic approaches could inhibit prostate tumor metabolism and block PCa metastasis. RESULTS Prostate tumor samples had more than twofold higher LXR target gene expression than normal prostate samples. Expression of LXR β positively correlated with the expression of lipid synthesis genes SREBP1c, FASN, and SCD1 (pearson r=.93, p=.03) that drive cancer cell metabolic activity. LXR expression positively correlated with androgen independent growth, resistance to chemotherapy, and increased risk of metastatic recurrence. Patients with primary tumors with relatively low LXR expression had a maximum recurrence free survival of 80 months compared to patients with high LXR expression of 15 months. LXR expression in a number of PCa cell lines also showed correlation with metastatic potential. The LXR inverse agonist SR9243, a pharmacologically active compound that suppresses LXR transcriptional activity, potently inhibited PCa tumor growth. CONCLUSIONS Results suggest LXR signaling may be hijacked by oncogenic signaling leading to upregulation of lipogenesis gene expression in prostate cancer cells that helps promote androgen independent metastatic disease. © 2018FiguresReferencesRelatedDetails Volume 199Issue 4SApril 2018Page: e939-e940 Advertisement Copyright & Permissions© 2018MetricsAuthor Information Allison May More articles by this author Suomia Abuirqeba More articles by this author Zachary Hamilton More articles by this author Colin Flaveny More articles by this author Sameer Siddiqui More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

MicroRNA-221 may be involved in lipid metabolism in mammary epithelial cells.

Milk lipids, important for infant growth and development, are produced and secreted by mammary gland under the regulation of steroid hormones, growth factors, and microRNAs (miRNAs). miR-221 has been identified in milk and adipocytes and it plays important roles in regulating normal mammary epithelial hierarchy and breast cancer stem cells; however, its roles in lipid metabolism in mammary epithelial cells (MECs), the cells of lipid synthesis and secretion, are as yet unknown. Through overexpression or inhibition of miR-221 expression, we found that it regulated lipid metabolism in MECs and was expressed differentially at various stages during murine mammary gland development. Inhibition of miR-221 expression increased lipid content in MECs through elevation of the lipid synthesis enzyme FASN, while overexpression of miR-221 reduced MEC lipid content. Moreover, the steroid hormones estradiol and progesterone decreased miR-221 expression with a subsequent increase in lipid formation in MECs. The expression of miR-221 was lower during lactation, which suggests that it may be involved in milk production. Therefore, miR-221 might be a useful target for influencing milk lipid production.

Impaired Skin Barrier Due to Sebaceous Gland Atrophy in the Latent Stage of Radiation-Induced Skin Injury: Application of Non-Invasive Diagnostic Methods.

Radiation-induced skin injury can take the form of serious cutaneous damage and have specific characteristics. Asymptomatic periods are classified as the latent stage. The skin barrier plays a critical role in the modulation of skin permeability and hydration and protects the body against a harsh external environment. However, an analysis on skin barrier dysfunction against radiation exposure in the latent stage has not been conducted. Thus, we investigated whether the skin barrier is impaired by irradiation in the latent stage and aimed to identify the molecules involved in skin barrier dysfunction. We analyzed skin barrier function and its components in SKH1 mice that received 20 and 40 Gy local irradiation. Increased transepidermal water loss and skin pH were observed in the latent stage of the irradiated skin. Skin barrier components, such as structural proteins and lipid synthesis enzymes in keratinocyte, increased in the irradiated group. Interestingly, we noted sebaceous gland atrophy and increased serine protease and inflammatory cytokines in the irradiated skin during the latent period. This finding indicates that the main factor of skin barrier dysfunction in the latent stage of radiation-induced skin injury is sebaceous gland deficiency, which could be an intervention target for skin barrier impairment.

A multi-omics analysis reveals metabolic reprogramming in THP-1 cells upon treatment with the contact allergen DNCB

Dendritic cell (DC) activation by contact allergens is one of the key steps in the development of allergic contact dermatitis (ACD). Recent evidence suggests that metabolic reprogramming is a prerequisite for the activation of DCs, macrophages and monocytes. Therefore, we used an integrated approach by combining proteomics and metabolomics to investigate the metabolism of human THP-1 cells in response to the strong contact allergen, 2,4-dinitrochlorobenzene (DNCB). Cells were treated with 5, 10 and 20μM DNCB for 4, 8, and 24h, respectively. Using a targeted metabolomics approach, we quantified levels of 188 endogenous metabolites, among them phospholipids, acylcarnitines, amino acids and hexoses. In addition, proteomic changes were analyzed using an untargeted quantitative approach based on stable isotope labeling with amino acids in cell culture (SILAC). We detected several alterations in the metabolome and consistently in the proteome indicating metabolic reprogramming of THP-1 cells by DNCB. In particular, we found an increase in phospholipids that was accompanied by an up-regulation of fatty acid synthase (FAS), a key enzyme in lipid synthesis.

Serial-omics of P53\u2212/\u2212, Brca1\u2212/\u2212 Mouse Breast Tumor and Normal Mammary Gland

This study demonstrates a liquid-liquid extraction for the sequential tandem mass spectrometry (LC-MS/MS) analysis of non-polar lipids, polar metabolites, proteins and phosphorylation sites from a single piece of tissue. Extraction of 10 mg BRCA−/−, p53−/− breast tumor tissue or normal mammary gland tissue with methyl-tert-butyl ether (MTBE) results in three phases: an upper non-polar phase containing 1,382 lipids, a lower polar phase with 805 metabolites and a precipitated protein pellet with 4,792 proteins with 1,072 phosphorylation sites. Comparative analysis revealed an activated AKT-mTOR pathway in tumors. Tumors also showed a reduction of phosphorylation sites involved in transcription and RNA splicing and decreased abundance of enzymes in lipid synthesis. Analysis of polar metabolites revealed a reduction in glycolysis, pentose phosphate pathway, polyamines and nucleotides, but an increase in TCA and urea cycle intermediates. Analysis of lipids revealed a shift from high triglycerides in mammary gland to high phospholipid levels in tumors. The data were integrated into a model showing breast tumors exhibit features on the proteomic, lipidomic and metabolomic level that are distinct from normal breast tissue. Our integrative technique lends itself to samples such as tumor biopsies, dried blood spots and fluids including urine and CSF to develop biomarkers of disease.

Activation of the STING-IRF3 pathway promotes hepatocyte inflammation, apoptosis and induces metabolic disorders in nonalcoholic fatty liver disease

BackgroundNonalcoholic fatty liver disease (NAFLD) is a common result of obesity and metabolic syndrome. Hepatocyte injury and metabolic disorders are hallmarks of NAFLD. Stimulator of interferon genes (STING) and its downstream factor interferon regulatory factor 3 (IRF3) trigger inflammatory reaction in response to the presence of cytosolic DNA. STING has recently been shown to play an important role in early alcoholic liver disease. However, little is known about the role of STING-IRF3 pathway in hepatocyte injury. Here, we aimed to examine the effect of STING-IRF3 pathway on hepatocyte metabolism, inflammation and apoptosis. MethodsWe examined the activation of the STING-IRF3 pathway, a high-fat diet (HFD)-induced obese mouse model, and determined the role of this pathway in a free fatty acid (FFA)-induced hepatocyte inflammatory response, injury, and dysfunction in L-O2 human liver cells. ResultsSTING and IRF3 were upregulated in livers of HFD-fed mice and in FFA-induced L-O2 cells. Knocking down either STING or IRF3 led to a significant reduction in FFA-induced hepatic inflammation and apoptosis, as evidenced by modulation of the nuclear factor κB (NF-κB) signaling pathway, inflammatory cytokines, and apoptotic signaling. Additionally, STING/IRF3 knockdown enhanced glycogen storage and alleviated lipid accumulation, which were found to be associated with increased expression of hepatic enzymes in glycolysis and lipid catabolism, and attenuated expression of hepatic enzymes in gluconeogenesis and lipid synthesis. ConclusionsOur results suggest that the STING-IRF3 pathway promotes hepatocyte injury and dysfunction by inducing inflammation and apoptosis and by disturbing glucose and lipid metabolism. This pathway may be a novel therapeutic target for preventing NAFLD development and progression.

MiR-15b negatively correlates with lipid metabolism in mammary epithelial cells.

Mammary epithelial cells are regulated by steroid hormones, growth factors, and even microRNAs. miR-15b has been found to regulate lipid metabolism in adipocytes; however, its effects on lipid metabolism in mammary epithelial cells, the cells of lipid synthesis and secretion, are as yet unknown. The main purpose of this investigation was to explore the effect of miR-15b on lipid metabolism in mammary epithelial cells, along with the underlying mechanisms. miR-15b was overexpressed or inhibited by miRNA mimics or inhibitors; subsequently, lipid formation in mammary epithelial cells, and proteins related to lipid metabolism, were investigated. Through overexpression or inhibition of miR-15b expression, the current investigation found that miR-15b downregulates lipid metabolism in mammary epithelial cells and is expressed differentially at various stages of mouse and goat mammary gland development. Inhibition of miR-15b expression increased lipid content in mammary epithelial cells through elevation of the lipid synthesis enzyme fatty acid synthetase (FASN), and overexpression of miR-15b reduced lipid content in mammary epithelial cells with decreasing levels of FASN. Moreover, the steroid hormones estradiol and progesterone decreased miR-15b expression with a subsequent increase in lipid formation in mammary epithelial cells. The expression of miR-15b was lower during lactation and negatively correlated with lipid synthesis proteins, which suggests that it may be involved in lipid synthesis and milk production. miR-15b might be a useful target for altering lipid production and milk yield.

Abstract 4406: Cullin3-KLHL25 ubiquitin ligase targets ACLY for degradation to inhibit lipid synthesis and tumor progression

Abstract Increased lipid synthesis is a key characteristic of many cancers, which is critical for cancer progression. As a key enzyme in lipid synthesis, ACLY (ATP citrate lyase) converts citrate in the cytosol to acetyl-CoA, which is a precursor for lipid synthesis. ACLY is frequently overexpressed or activated in cancer, which plays an important role in promoting lipid synthesis and cancer progression. Currently, the mechanism underlying ACLY overexpression and increased lipid synthesis in cancer is poorly understood. Cullin3 (CUL3) is a core protein for CUL3-RING ubiquitin ligase complex. CUL3 has been recently reported to be a tumor suppressor and its expression is frequently down-regulated in lung cancer. The mechanism of CUL3 in tumor suppression is not well-understood. In this study, we found that CUL3 interacted with ACLY through its adaptor protein KLHL25 to ubiquitinate and degrade ACLY in cells. Ectopic CUL3 expression in lung cancer cells greatly inhibited lipid synthesis, cell proliferation and tumor growth, whereas knockdown of endogenous CUL3 in lung cancer cells greatly promoted lipid synthesis, cell proliferation and tumor growth. Furthermore, negative regulation of ACLY contributes greatly to these functions of CUL3. Supplementation of lipid metabolites in culture medium, such as oleic acid, mevalonate and acetate, significantly reduced the inhibitory effect of CUL3 on proliferation and colony formation of cancer cells. SB-204990, a small-molecule ACLY inhibitor greatly abolished the promoting effect of CUL3 down-regulation on lipid synthesis, cell proliferation and tumor growth. In addition, we identified K540, K546 and K554 of ALCY as major ubiquitination sites of CUL3. Mutations of K540, K546 and K554 (K540R/K546R/K554R) greatly reduced CUL3-mediated ubiquitination and degradation of ACLY, and greatly compromised the inhibitory effect of CUL3 on tumor growth as well. Importantly, low CUL3 expression is significantly associated with high ACLY expression in clinical lung cancer specimens, and poor prognosis in lung cancer patients. In summary, our results identified CUL3-KLHL25 ubiquitin ligase as a novel negative regulator for ACLY and lipid synthesis, and demonstrated that decreased CUL3 expression is an important mechanism for increased ACLY expression and lipid synthesis in lung cancer. These results also revealed that negative regulation of ACLY and lipid synthesis is a novel and critical mechanism for CUL3 in tumor suppression. Citation Format: Cen Zhang, Juan Liu, Yuhan Zhao, Xuetian Yue, Hao Wu, Jun Li, Zhiyuan Shen, Bruce Haffty, Wenwei Hu, Zhaohui Feng. Cullin3-KLHL25 ubiquitin ligase targets ACLY for degradation to inhibit lipid synthesis and tumor progression [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 4406. doi:10.1158/1538-7445.AM2017-4406

MicroRNA-126 participates in lipid metabolism in mammary epithelial cells

Lipids are a major component of milk and are important for infant growth and development. MicroRNA-126 (miR-126) has previously been observed in mammary glands and adipocytes and is known to be involved in lipid metabolism during the process of atherosclerosis. However, it remains unknown whether miR-126 also participates in lipid metabolism in mammary luminal epithelial cells (MECs). In the current investigation, miR-126-3p inhibition stimulated lipid synthesis in MECs in part through increasing levels of the lipid synthesis enzymes FASN, ACSL1, and Insig1. Overexpression of miR-126-3p decreased lipid content in MECs with a reduction in FASN and Insig1. Furthermore, the expression of miR-126-3p was diminished by the steroid hormones estradiol and progesterone with a subsequent elevation of lipid formation in MECs. We also noted that miR-126-3p was expressed differentially at various stages of murine mammary gland development, exhibiting a negative correlation with FASN. Together these findings suggest that miR-126-3 might be involved in lipid metabolism in mammary gland.

The effects of arecoline on the lipid metabolism of 3T3-L1 adipocytes

To observe the effects of arecoline on lipid metabolism in 3T3-L1 adipocytes and explore its possible mechanisms. 3T3-L1 pre-adipocytes were induced into adipocytes with the classic "cocktail" method, subsequently, adipocytes were treated with arecoline at the concentrations of 0, 25, 50 and 100 μmol/L for 72 hours. After 72 hours, cell vability was measured with MTT method, lipid droplet accumulation in the cytoplasm was observed with oil red O staining, the protein expression of fatty acid synthase (FAS), adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) were detected by Western blot assay. There were a large number of lipid droplets in the cytoplasm in the differentiated 3T3-L1 adipocytes. MTT results showed that 0~100 μmol/L arecoline had no significant effect on cell vability; oil red O staining found arecoline reduced lipid amount in 3T3-L1 adipocytes; Western blot results showed that compared with 0 μmol/L arecoline group (the control group), arecoline significantly reduced the protein level of FAS and increased the protein levels of ATGL and HSL, and 50 μmol/L arecoline group was the most significant. Arecoline significantly increased lipolysis of 3T3-L1 adipocyte, which might be associated with decreased the FAS expression of key enzyme of lipid synthesis and increased the ATGL and HSL expression of key enzyme of adipolysis.

Local Burn Injury Promotes Defects in the Epidermal Lipid and Antimicrobial Peptide Barriers in Human Autograft Skin and Burn Margin

Burn injury increases the risk of morbidity and mortality by promoting severe hemodynamic shock and risk for local or systemic infection. Graft failure due to poor wound healing or infection remains a significant problem for burn subjects. The mechanisms by which local burn injury compromises the epithelial antimicrobial barrier function in the burn margin, containing the elements necessary for healing of the burn site, and in distal unburned skin, which serves as potential donor tissue, are largely unknown. The objective of this study was to establish defects in epidermal barrier function in human donor skin and burn margin, to identify potential mechanisms that may lead to graft failure and/or impaired burn wound healing. In this study, we established that epidermal lipids and respective lipid synthesis enzymes were significantly reduced in both donor skin and burn margin. We further identified diverse changes in the gene expression and protein production of several candidate skin antimicrobial peptides (AMPs) in both donor skin and burn margin. These results also parallel changes in cutaneous AMP activity against common burn wound pathogens, aberrant production of epidermal proteases known to regulate barrier permeability and AMP activity, and greater production of proinflammatory cytokines known to be induced by AMPs. These findings suggest that impaired epidermal lipid and AMP regulation could contribute to graft failure and infectious complications in subjects with burn or other traumatic injury.

Omental adipocytes enhance the invasiveness of gastric cancer cells by oleic acid-induced activation of the PI3K-Akt signaling pathway

A considerable number of patients with advanced gastric cancer have a clear predilection for metastasis to the great omentum, an organ mainly composed of adipose tissue. However, it remains unclear why tumor cells preferentially spread to and progress in the omentum. Here, we used a two-dimensional co-culture system to simulate the crosstalk between adipocytes and gastric cancer cells and showed that after co-culture with isolated omental adipocytes, gastric cancer cells exhibited a significant increase in lipid uptake and enhanced invasiveness. A lipidomic study showed that gastric cancer cells accumulated higher levels of oleic acid during the co-culture. By performing an assay of key enzymes in lipid synthesis, we demonstrated that the increased amount of oleic acid in gastric cancer cells mainly came from the adjacent adipocytes in the co-culture system. Furthermore, our data showed that at a certain concentration range, oleic acid treatment enhanced the invasiveness of gastric cancer cells in vitro and in a CAM assay, through the PI3K/Akt pathway, with the associated increased expression of the key pro-invasion factor MMP-2. Taken together, our results demonstrated that adipocytes may serve as an exogenous source of oleic acid that promotes gastric cancer cell invasion through the PI3K/Akt signaling pathway.

HPLC-Based Mass Spectrometry Characterizes the Phospholipid Alterations in Ether-Linked Lipid Deficiency Models Following Oxidative Stress.

Despite the fact that the discovery of ether-linked phospholipids occurred nearly a century ago, many unanswered questions remain concerning these unique lipids. Here, we characterize the ether-linked lipids of the nematode with HPLC-MS/MS and find that more than half of the phosphoethanolamine-containing lipids are ether-linked, a distribution similar to that found in mammalian membranes. To explore the biological role of ether lipids in vivo, we target fatty acyl-CoA reductase (fard-1), an essential enzyme in ether lipid synthesis, with two distinct RNAi strategies. First, when fard-1 RNAi is initiated at the start of development, the treated animals have severely reduced ether lipid abundance, resulting in a shift in the phosphatidylethanolamine lipid population to include more saturated fatty acid chains. Thus, the absence of ether lipids during development drives a significant remodeling of the membrane landscape. A later initiation of fard-1 RNAi in adulthood results in a dramatic reduction of new ether lipid synthesis as quantified with 15N-tracers; however, there is only a slight decrease in total ether lipid abundance with this adult-only fard-1 RNAi. The two RNAi strategies permit the examination of synthesis and ether lipid abundance to reveal a relationship between the amount of ether lipids and stress survival. We tested whether these species function as sacrificial antioxidants by directly examining the phospholipid population with HPLC-MS/MS after oxidative stress treatment. While there are significant changes in other phospholipids, including polyunsaturated fatty acid-containing species, we did not find any change in ether-linked lipids, suggesting that the role of ether lipids in stress resistance is not through their general consumption as free radical sinks. Our work shows that the nematode will be a useful model for future interrogation of ether lipid biosynthesis and the characterization of phospholipid changes in various stress conditions.

5,7-Dimethoxyflavone Attenuates Obesity by Inhibiting Adipogenesis in 3T3-L1 Adipocytes and High-Fat Diet-Induced Obese C57BL/6J Mice.

The antiobesity effect of 5,7-dimethoxyflavone (DMF) was evaluated in 3T3-L1 adipocytes and high-fat diet (HFD)-induced obese C57BL/6J mice. The accumulation of lipid droplets and triglycerides in adipocytes was dose dependently suppressed by DMF through inhibition of adipogenesis. DMF downregulated the adipogenic transcription factors (peroxisome proliferator-activated receptor [PPAR]γ, CCAAT/enhancer binding protein [C/EBP]α, and sterol regulatory element-binding protein-1c [SREBP-1c]) and lipid synthesis enzymes (fatty acid synthase [FAS], acetyl-CoA carboxylase [ACC], lipoprotein lipase [LPL], and HMG-CoA reductase [HMGR]). AMP-activated protein kinase (AMPK) and AMPK related lipolytic proteins in differentiated adipocytes were activated by DMF. In the animal model, oral administration of DMF (50 mg/kg/day for 6 weeks) significantly decreased body weight gain without affecting food intake. Elevated serum levels of total cholesterol and low-density lipoprotein cholesterol were suppressed by DMF. Fat pad masses were reduced in DMF-treated obese mice, as evidenced by reduced adipocyte size. DMF altered the expression of adipogenic transcription factors in epididymal fat tissue. In addition, DMF attenuated HFD-induced nonalcoholic fatty liver disease by decreasing hepatic triglyceride accumulation. Overall, these results suggest that DMF is a potential natural agent for attenuating obesity and other obesity-related metabolic syndromes.

Esculetin prevents non-alcoholic fatty liver in diabetic mice fed high-fat diet

This study investigated the effects and mechanism of esculetin (6,7-dihydroxycoumarin) on non-alcoholic fatty liver in diabetic mice fed high-fat diet (HFD). The diabetic mice model was induced by injection of streptozotocin, after which they were fed HFD diet with or without esculetin for 11 weeks. Non-diabetic mice were provided a normal diet. Diabetes induced hepatic hypertrophy, lipid accumulation and droplets; however, esculetin reversed these changes. Esculetin treatment in diabetic mice fed HFD significantly down-regulated expression of lipid synthesis genes (Fasn, Dgat2 and Plpp2) and inflammation genes (Tlr4, Myd88, Nfkb, Tnfα and Il6). Moreover, the activities of hepatic lipid synthesis enzymes (fatty acid synthase and phosphatidate phosphohydrolase) and gluconeogenesis enzyme (glucose-6-phosphatase) in the esculetin group were decreased compared with the diabetic group. In addition, esculetin significantly reduced blood HbA1c, serum cytokines (TNF-α and IL-6) and chemokine (MCP-1) levels compared with the diabetic group without changing the insulin content in serum and the pancreas. Hepatic SOD activity was lower and lipid peroxidation level was higher in the diabetic group than in the normal group; however, esculetin attenuates these differences. Overall, these results demonstrated that esculetin supplementation could protect against development of non-alcoholic fatty liver in diabetes via regulation of lipids, glucose and inflammation.

Cullin3-KLHL25 ubiquitin ligase targets ACLY for degradation to inhibit lipid synthesis and tumor progression.

Increased lipid synthesis is a key characteristic of many cancers that is critical for cancer progression. ATP-citrate lyase (ACLY), a key enzyme for lipid synthesis, is frequently overexpressed or activated in cancer to promote lipid synthesis and tumor progression. Cullin3 (CUL3), a core protein for the CUL3-RING ubiquitin ligase complex, has been reported to be a tumor suppressor and frequently down-regulated in lung cancer. Here, we found that CUL3 interacts with ACLY through its adaptor protein, KLHL25 (Kelch-like family member 25), to ubiquitinate and degrade ACLY in cells. Through negative regulation of ACLY, CUL3 inhibits lipid synthesis, cell proliferation, and xenograft tumor growth of lung cancer cells. Furthermore, ACLY inhibitor SB-204990 greatly abolishes the promoting effect of CUL3 down-regulation on lipid synthesis, cell proliferation, and tumor growth. Importantly, low CUL3 expression is associated with high ACLY expression and poor prognosis in human lung cancer. In summary, our results identify CUL3-KLHL25 ubiquitin ligase as a novel negative regulator for ACLY and lipid synthesis and demonstrate that decreased CUL3 expression is an important mechanism for increased ACLY expression and lipid synthesis in lung cancer. These results also reveal that negative regulation of ACLY and lipid synthesis is a novel and critical mechanism for CUL3 in tumor suppression.

Seipin is required for converting nascent to mature lipid droplets.

How proteins control the biogenesis of cellular lipid droplets (LDs) is poorly understood. Using Drosophila and human cells, we show here that seipin, an ER protein implicated in LD biology, mediates a discrete step in LD formation-the conversion of small, nascent LDs to larger, mature LDs. Seipin forms discrete and dynamic foci in the ER that interact with nascent LDs to enable their growth. In the absence of seipin, numerous small, nascent LDs accumulate near the ER and most often fail to grow. Those that do grow prematurely acquire lipid synthesis enzymes and undergo expansion, eventually leading to the giant LDs characteristic of seipin deficiency. Our studies identify a discrete step of LD formation, namely the conversion of nascent LDs to mature LDs, and define a molecular role for seipin in this process, most likely by acting at ER-LD contact sites to enable lipid transfer to nascent LDs.