De Novo Lipogenesis Research Articles

Multi-substrate Metabolic Tracing Reveals Marked Heterogeneity and Dependency on Fatty Acid Metabolism in Human Prostate Cancer.

Prostate cancer utilizes multiple substrates to fuel energy requirements, yet pharmacologic targeting of fatty acid uptake and oxidation reveals metabolic dependencies in localized and metastatic tumors.

Naringin attenuates fructose-induced NAFLD progression in rats through reducing endogenous triglyceride synthesis and activating the Nrf2/HO-1 pathway.

Background: Excessive fructose consumption causes hepatic lipid accumulation via increased triglyceride (TG) synthesis, leading to the development and progression of non-alcoholic fatty liver disease (NALFD). Naringin, a flavanone glycoside found in citrus fruit, has antioxidant and hypolipidemic properties. Therefore, the aim of this study was to investigate the effect of naringin on fructose-induced NAFLD in rats and the possible underlying mechanism. Methods: Male Sprague Dawley rats were given 10% (w/v) fructose in drinking water for 12weeks. Naringin (100mg/kg/day) was administered orally to rats for the last 4weeks of fructose overload. After 12weeks of treatment, the hepatic lipid content was determined. In addition, the expression of proteins involved in de novo lipogenesis (DNL) and TG synthesis as well as antioxidant and inflammatory mediators in the liver were examined by western blot analysis. Results: Treatment of fructose-fed rats with naringin significantly decreased the hepatic TG and cholesterol content as well as serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities. Naringin treatment also decreased the hepatic expression of carbohydrate response element binding protein (ChREBP), sterol regulatory element-binding protein-1c (SREBP-1c) and nuclear SREBP-1c (nSREBP-1c) as well as enzymes involved in DNL (acetyl CoA carboxylase [ACC] and fatty acid synthase [FAS]) and an enzyme involved in TG synthesis (glycerol-3-phosphate acyltransferase 1 [GPAT-1] and diacylglycerol acyltransferase2 [DGAT2]) in fructose-fed rats. In addition, naringin induced a significant decrease in the hepatic expression of nuclear factor kappa B (NF-κB) and tumor necrosis factor α (TNF-α). Furthermore, naringin administration restored the expression of the antioxidant mediators nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and heme oxygenase-1 (HO-1) in the liver of fructose-fed rats. Conclusion: These results demonstrate that oral administration of naringin protects against fructose-induced hepatic steatosis by decreasing DNL and TG synthesis. In addition, naringin could prevent NAFLD progression via targeting the Nrf2/HO-1 and the NF-κB/TNF-α pathways.

Diosgenin Ameliorated Type II Diabetes-Associated Nonalcoholic Fatty Liver Disease through Inhibiting De Novo Lipogenesis and Improving Fatty Acid Oxidation and Mitochondrial Function in Rats

Diosgenin (DIO) is a dietary and phytochemical steroidal saponin representing multiple activities. The present study investigated the protective effect of DIO on type II diabetes-associated nonalcoholic fatty liver disease (D-NAFLD). The rat model was established by high-fat diet and streptozotocin injection and then administered DIO for 8 weeks. The results showed that DIO reduced insulin resistance index, improved dyslipidemia, and relieved pancreatic damage. DIO decreased hepatic injury markers, including aspartate aminotransferase (AST) and alanine aminotransferase (ALT). H&E staining showed that DIO relieved hepatic lipid deposition. Mechanistically, DIO inhibited hepatic de novo lipogenesis (DNL) and increased fatty acid β-oxidation (FAO) through regulation of the AMPK-ACC/SREBP1 pathway. Endoplasmic reticulum (ER) stress was inhibited by DIO through regulation of PERK and IRE1 arms, which may then inhibit DNL. DIO also decreased reactive oxygen species (ROS) and enhanced the antioxidant capacity via an increase in Superoxide dismutase (SOD), Catalase (CAT), and Glutathione peroxidase (GPx) activities. The mitochondria are the site for FAO, and ROS can damage mitochondrial function. DIO relieved mitochondrial fission and fusion disorder by inhibiting DRP1 and increasing MFN1/MFN2 expressions. Mitochondrial apoptosis was then inhibited by DIO. In conclusion, the present study suggests that DIO protects against D-NAFLD by inhibiting DNL and improving FAO and mitochondrial function.

Integration of Liver Glycogen and Triglyceride NMR Isotopomer Analyses Provides a Comprehensive Coverage of Hepatic Glucose and Fructose Metabolism.

Dietary glucose and fructose are both efficiently assimilated by the liver but a comprehensive measurement of this process starting from their conversion to sugar phosphates, involvement of the pentose phosphate pathway (PPP), and conversion to glycogen and lipid storage products, remains incomplete. Mice were fed a chow diet supplemented with 35 g/100 mL drinking water of a 55/45 fructose/glucose mixture for 18 weeks. On the final night, the sugar mixture was enriched with either [U-13C]glucose or [U-13C]fructose, and deuterated water (2H2O) was also administered. 13C-isotopomers representing newly synthesized hepatic glucose-6-phosphate (glucose-6-P), glycerol-3-phosphate, and lipogenic acetyl-CoA were quantified by 2H and 13C NMR analysis of post-mortem liver glycogen and triglyceride. These data were applied to a metabolic model covering glucose-6-P, PPP, triose-P, and de novo lipogenesis (DNL) fluxes. The glucose supplement was converted to glucose-6-P via the direct pathway, while the fructose supplement was metabolized by the liver to gluconeogenic triose-P via fructokinase-aldolase-triokinase. Glucose-6-P from all carbohydrate sources accounted for 40-60% of lipogenic acetyl-CoA and 10-12% was oxidized by the pentose phosphate pathway (PPP). The yield of NADPH from PPP flux accounted for a minority (~30%) of the total DNL requirement. In conclusion, this approach integrates measurements of glucose-6-P, PPP, and DNL fluxes to provide a holistic and informative assessment of hepatic glucose and fructose metabolism.

OR24-5 Zebrafish in Utero Glucose Exposure Induces Lipid Dysregulation That Is Abrogated by Acetyl CoA Carboxylase or Glycolysis Inhibition

Abstract Background and Aim One in ten pregnancies suffer from Gestational Diabetes Mellitus (GDM). GDM exposes fetus to high uterine glucose that causes fetal hyperglycemia. At birth Fetal hyperglycemia results in hypoglycemia, macrosomia, and larger than normal infants and these infants are predisposed to a number of metabolic disorders such as obesity, Type 2 Diabetes and non-alcoholic fatty liver disease (NAFLD) in adulthood. Although in-utero glucose exposure provides evidence for fetal lipid dysregulation linked to metabolic disorders in adults, the molecular mechanisms are still unclear. Increase in circulating insulin and glucose are implicated in the enhanced activation of hepatic De novo lipogenesis (DNL) in dyslipidemia, hence, we aim to investigate the potential beneficial effect of the pharmacological inhibition of DNL or glycolysis in our well-characterized zebrafish model of fetal hyperglycemia that mimics the metabolic disorders in human GDM against lipid derangement mediated by excess glucose in embryos in a short term and avoid the long-term outcome of obesity. Methods We developed a zebrafish model of fetal hyperglycemia by exposing embryos to high glucose (4.5% w/v) during the last day of embryogenesis from 96 to 120 hours post-fertilization (hpf). Glucose level was detected in embryo homogenates by glucometer. Insulin expression was visualized by whole-mount in-situ Hybridization. Gene expression of glycolytic (Hexokinase) and lipogenic [Acetyl-CoA Carboxylase (acca)] markers by RT-qPCR and malonyl CoA levels (product of DNL) by ELISA were also assessed. Lipid accumulation was detected by Oil-Red-O staining (ORO) and quantified by spectrophotometry. Pharmacological intervention using metformin or ND646 (known inhibitors of acca) or 2-Deoxyglucose, 2DG (Known inhibitor of Hexokinase) with glucose for 24hours were utilized to attenuate fetal hyperglycemia-mediated lipid accumulation in embryos. Results Zebrafish embryos exposed to high glucose for 24 hours are transiently hyperglycemic while normoglycemia is restored 24 hours after removal from glucose media. At 120 hpf embryos exposed to high-glucose demonstrated increased insulin, hexokinase, and acca expression compared to untreated controls. We also observed a significant reduction in malonyl CoA levels in ND 646 and metformin cotreated embryos with glucose compared to controls. Interestingly, quantification of ORO staining revealed a significant increase in lipid deposition in glucose treated embryos compared to controls at 120 hpf (0.2±0.01 vrs 0.13±0.005), which was significantly attenuated in embryos co-treated with glucose and 2-DG- (0.15±0.003) or metformin- (0.11±0.007) compared to glucose-treated embryos. Similarly, a moderate reduction in ORO staining was observed in embryos that were co-treated with glucose and ND646 (0.17 ± 0.006). Conclusion and significance Together our results show that embryonic glucose exposure leads to increased lipid accumulation which can be rescued by blocking glycolysis or de novo lipogenesis. Intervening glycolysis and de novo lipogenesis could be a promising therapeutic approach for modulating fetal hyperglycemia-related lipid dysregulations. Presentation: Monday, June 13, 2022 12:00 p.m. - 12:15 p.m.

PSUN123 Increased Expression of Insulin Signaling Intermediates After Six-Months Of Medical Care In Women With Obesity And Polycystic Ovary Syndrome

Abstract Background Recently an androgen-induced obesity-independent mechanism of insulin resistance in a mouse model mimicking lean polycystic ovary syndrome (PCOS) was discovered. To date there is little to no data on the mechanism of insulin resistance or molecular insulin signaling in adipose tissue of women with PCOS undergoing Vertical Sleeve Gastrectomy (VSG). Does the mechanism of androgen receptor (AR)-mediated regulation of insulin signaling seen in the lean PCOS mouse model occur in adipose tissue of women with obesity and PCOS? Objective We hypothesize that in women with obesity and PCOS, those with higher levels of free androgen index will display more dysregulation in the insulin signaling pathway in adipose tissue. More specifically, we believe that visceral more than subcutaneous adipose tissue in the women in the study will display more dysregulation; and lastly that VSG will alleviate insulin signaling dysregulation. Briefly, insulin activates insulin receptor (IR) which leads to activation of phospho-AKT which increases phosphorylated forkhead box 01 (p-FOXO1, gluconeogenesis regulation) and transcriptionally regulates acetyl co-A carboxylase (ACC, de novo lipogenesis (DNL) regulation). Methods This is a nested mechanistic study within a randomised controlled clinical trial. We performed molecular analyses (Western blots for protein and qPRC for mRNA expression, respectively, n = 3-4/group) exploring intermediates in the insulin signaling pathway (IR, p-AKT, p-FOXO1, and ACC) in (i) visceral and subcutaneous (SubQ) adipose tissue from women with obesity and PCOS before VSG bariatric surgery (n = 3/group); and (ii) SubQ WAT from women with obesity and PCOS at baseline and six-months after medical intervention with metformin (MTF) and lifestyle modification. Results Subcutaneous (SubQ) white adipose tissue (WAT) displayed similar levels of p-ACC compared to visceral WAT from women pre-VSG. Six months of medical care increased p-ACC in SubQ WAT by 5-fold compared to baseline. IR displayed similar expression in the visceral compared to SubQ WAT in women pre-VSG. IR expression increased by 20-fold at 6-months of medical care compared to baseline in SubQ WAT. p-FOXO1 displayed similar expression in the visceral compared to SubQ WAT. However, p-FOXO1 was decreased at 6-months of medical care compared to baseline. p-AKT levels were similar in visceral compared to SubQ WAT pre-VSG. However, p-AKT levels were significantly increased by 4-fold at 6-months of medical care compared to baseline. Conclusion None of the insulin signaling intermediates measured were different in visceral compared to SubQ in women with obesity and PCOS. Additionally, the findings indicated lowered DNL, lowered regulation of gluconeogenic genes and thus lowered gluconeogenesis, and increased insulin action in SubQ WAT in women with obesity and PCOS after 6-months of medical care. Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.

RF32 | PSUN44 CARF Regulates Non-Alcoholic Fatty Liver Diseases (NAFLD) by Controlling ER Stress and Lipogenesis in Hepatic Cells.

Abstract Background Sedentary lifestyles and changes in diet are fueling the worldwide epidemic of obesity and the prevalence of NAFLD and insulin resistance (IR). It has been predicted that NAFLD and its more advanced form, nonalcoholic steatohepatitis (NASH) will be the next epidemic in chronic liver diseases, and NAFLD/NASH will soon replace viral hepatitis as the primary cause of end-stage liver failure and transplantation. NAFLD is a significant risk factor for IR and cardiovascular diseases, and it highlights the importance of finding a way to control the epidemic. CARF is a multifunctional stress-responsive gene and was found to be reduced in response to metabolic stress in the fatty liver of diet-induced obesity mice (DIO). We also showed that CARF expression was down-regulated in palmitate (PA)-treated HepG2 cells. In this study, we aim to understand the consequences of the reduced expression of CARF on the development of NAFLD. Methods We performed RNA seq, RT-PCR and western blotting (WB) to evaluate the effect of CARF knockdown on lipid metabolism in HepG2 cells. Differentially expressed genes were analyzed by gene sort enrichment analysis (GSEA) and Ingenuity Pathway Analysis (IPA) to identify the metabolic pathways affected by CARF depletion. Apoptosis was assessed by TUNEL assay. To induce ER stress, HepG2 cells were treated with thapsigargin and evaluated its effect on CARF. Results By performing Sh-RNA mediated CARF knockdown, RNA-seq analysis, RT-PCR, western blotting (WB), we were able to show that ER-stress and de-novo lipogenesis pathways were significantly affected in HepG2 cells. We showed that GRP78, CHOP, PERK, ERN1a, genes associated with ER-stress were upregulated in CARF-depleted HepG2 cells. Additionally, thapsigargin-induced ER stress was found to reduce the expression of CARF along with the increased expression of ER stress marker genes. We also showed that overexpression of CARF mitigated the thapsigargin-induced ER stress suggesting that CARF protects against ER stress in HepG2 cells. In addition, the genes associated with triglyceride biosynthesis GPAT3, GPAM were significantly upregulated, indicating that lipogenesis was triggered by silencing of CARF in HepG2 cells. BODIPY staining and TG assay confirmed that silencing of CARF enhanced triglyceride biosynthesis in HepG2 cells. Furthermore, we showed that the expression of antioxidant genes GPX2, GPX3, and TXRND3 decreased, resulting in enhanced oxidative stress and higher apoptosis in CARF depleted cells. Conclusion We identified novel roles of CARF regulating cellular ER-Stress, lipid metabolism, and oxidative stress, and its impairment in response to metabolic stress could lead to the development of NAFLD in obese patients with metabolic abnormalities. Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m., Monday, June 13, 2022 12:42 p.m. - 12:47 p.m.

Epstein-Barr Virus-Encoded MicroRNA-BART18-3p Promotes Colorectal Cancer Progression by Targeting De Novo Lipogenesis.

The Epstein-Barr virus (EBV) genome encodes a cluster of 22 viral microRNAs, called miR-BamHI-A rightward transcripts (miR-BARTs), which are shown to promote the development of cancer. Here, this study reports that EBV-miR-BART18-3p is highly expressed in colorectal cancer (CRC) and is closely associated with the pathological and advanced clinical stages of CRC. Ectopic expression of EBV-miR-BART18-3p leads to increased migration and invasion capacities of CRC cells in vitro and causes tumor metastasis in vivo. Mechanistically, EBV-miR-BART18-3p activates the hypoxia inducible factor 1 subunit alpha/lactate dehydrogenase A axis by targeting Sirtuin, which promotes lactate accumulation and acetyl-CoA production in CRC cells under hypoxic condition. Increased acetyl-CoA utilization subsequently leads to histone acetylation of fatty acid synthase and fatty acid synthase-dependent fat synthesis, which in turn drives de novo lipogenesis. The oncogenic role of EBV-miR-BART18-3p is confirmed in the patient-derived tumor xenograft mouse model. Altogether, the findings define a novel mechanism of EBV-miR-BART18-3p in CRC development through the lipogenesis pathway and provide a potential clinical intervention target for CRC.

SLC16A7 Promotes Triglyceride Deposition by De Novo Lipogenesis in Chicken Muscle Tissue

Triglyceride (TG) content in chicken muscle tissue signifies intramuscular fat (IMF) content, which is important for improving meat quality. However, the genetic basis of TG deposition in chicken is still unclear. Using 520 chickens from an artificially selected line with significantly increased IMF content and a control line, a genome-wide association study (GWAS) with TG content reports a region of 802 Kb located in chromosome 1. The XP-EHH and gene expression analysis together reveal that the solute carrier family 16 member A7 (SLC16A7) gene is the key candidate gene associated with TG content in chicken muscle tissue. Furthermore, the weighted gene co-expression network analysis (WGCNA) confirmed the regulatory effects of SLC16A7 on promoting TG deposition by de novo lipogenesis (DNL). Functional verification of SLC16A7 in vitro also supports this view, and reveals that this effect mainly occurs in myocytes. Our data highlight a potential IMF deposition pathway by DNL, induced by SLC16A7 in chicken myocytes. These findings will improve the understanding of IMF regulation in chicken and guide the formulation of breeding strategies for high-quality chicken.

Inhibition on XBP1s-driven lipogenesis by Qushi Huayu Decoction contributes to amelioration of hepatic steatosis induced by fructose

Ethnopharmacological relevanceQushi Huayu Decoction (QHD) is a traditional Chinese medicine formula consisting of five herbs, which has been used for non-alcoholic fatty liver disease (NAFLD) treatment in clinic for decades in China and validated in several NAFLD animal models. The hepatic de novo lipogenesis (DNL) is enhanced greatly to contribute to steatosis in NAFLD. The spliced form of X-box binding protein 1 (XBP1s) initiates DNL independently of sterol regulatory element-binding protein (SREBP) and carbohydrate-responsive element-binding protein (ChREBP). Aim of the studyTo disclose the mechanism of inhibition on hepatic DNL by QHD and the responsible compounds. MethodsThe effects of QHD on hepatic DNL were evaluated in mice induced by high-fructose diet (HFru). The effects of the serum-absorbed compounds of QHD on XBP1s were evaluated in HepG2 cells induced by tunicamycin. Hepatic histology, triglyceride (TG) and nonesterified fatty acids were observed. Hepatic apolipoprotein B100 and very low-density lipoprotein were measured to reflect lipid out-transport. The mRNA expression of XBP1s and its target genes were detected by real-time polymerase chain reaction. The protein expression of TG synthetases and DNL enzymes, and inositol requirement enzyme 1 alpha (IRE1α), phosphorylated IRE1α and XBP1s were detected in liver tissue and HepG2 cells by western-blot. The binding activity of SREBP1, protein expression of ChREBP and XBP1s were detected in the nuclear extracts of liver tissue. ResultsDynamical observing suggested feeding with HFru for 2 weeks was sufficient to induce hepatic lipogenesis and XBP1s. QHD ameliorated liver steatosis without enhancing out-transport of lipids, accompanied with more inhibitory effects on DNL enzymes than TG synthetases. QHD inhibits the nuclear XBP1s without affecting ChREBP and SREBP1. In QHD, chlorogenic acid, geniposide and polydatin inhibit lipogenesis initiated by XPB1s. ConclusionQHD probably decreases hepatic DNL by inhibiting XBP1s independent of SREBP1 and ChREBP. Chlorogenic acid, geniposide and polydatin are the potential responsible compounds.

Acetyl Co-A Carboxylase Inhibition Halts Hyperglycemia Induced Upregulation of De Novo Lipogenesis in Podocytes and Proximal Tubular Cells.

The effect of glycemic stress on de novo lipogenesis (DNL) in podocytes and tubular epithelial cells is understudied. This study is aimed (A) to show the effect of glycemic stress on DNL, and (B) to assess the effect of acetyl-Co A (ACC) inhibition on halting upregulation of DNL, on the expression of other lipid regulatory genes in the DNL pathway, and on markers of fibrosis and apoptosis in podocytes and tubular epithelial cells. We used cultured mouse primary tubular epithelial cells, mouse proximal tubular (BUMPT) cells, and immortal mouse podocytes and measured their percentage of labeled 13C2-palmitate as a marker of DNL after incubation with 13C2 acetate in response to high glucose concentration (25 mM). We then tested the effect of ACC inhibition by complimentary strategies utilizing CRISPR/cas9 deletion or incubation with Acaca and Acacb GapmeRs or using a small molecule inhibitor on DNL under hyperglycemic concentration. Exposure to high glucose concentration (25 mM) compared to osmotic controlled low glucose concentration (5.5 mM) significantly increased labeled palmitate after 24 h up to 72 h in podocytes and primary tubular cells. Knocking out of the ACC coding Acaca and Acacb genes by CRISPR/cas9, downregulation of Acaca and Acacb by specific antisense LNA GapmeRs and inhibition of ACC by firsocostat similarly halted/mitigated upregulation of DNL and decreased markers of fibrosis and programmed cell death in podocytes and various tubular cells. ACC inhibition is a potential therapeutic target to mitigate or halt hyperglycemia-induced upregulation of DNL in podocytes and tubular cells.

Follistatin Alleviates Hepatic Steatosis in NAFLD via the mTOR Dependent Pathway.

In this study, we aimed to investigate the effect of follistatin (FST) on hepatic steatosis in NAFLD and the underlying mechanism, which has rarely been reported before. Liver samples from NAFLD patients and normal liver samples (from liver donors) were collected to investigate hepatic FST expression in humans. Additionally, human liver cells (LO2) were treated with free fatty acid (FFA) to induce lipid accumulation. Furthermore, lentivirus with FST overexpression or knockdown vectors were used to generate stable cell lines, which were subsequently treated with FFA or FFA and rapamycin. In the animal experiments, male C57BL/6J mice were fed with a high-fat diet (HFD) to induce NAFLD, after which the adeno-associated virus (AAV) gene vectors for FST overexpression were administered. In both cell culture and mice, we evaluated morphological changes and the protein expression of sterol regulatory element-binding protein1 (SREBP1), acetyl-CoA carboxylase1 (ACC1), carbohydrate-responsive element-binding protein (ChREBP), fatty acid synthase (FASN), and Akt/mTOR signaling. The body weight and serum parameters of the mice were also measured. Hepatic FST expression level was higher in NAFLD patients compared to normal samples. In LO2 cells, FST overexpression alleviated lipid accumulation and lipogenesis, whereas FST knockdown aggravated hepatic steatosis. FST could regulate Akt/mTOR signaling, and the mTOR inhibitor rapamycin abolished the effect of FST knockdown on hepatic de novo lipogenesis (DNL). Furthermore, FST expression was increased in HFD mice compared to the corresponding controls. FST overexpression in mice reduced body weight gain, hyperlipidemia, hepatic DNL, and suppressed Akt/mTOR signaling. Hepatic FST expression increases in NAFLD and plays a protective role in hepatic steatosis. FST overexpression gene therapy alleviates hepatic steatosis via the mTOR pathway.Therefore, gene therapy for FST is a promising treatment in NAFLD.

Lactation alters the relationship between liver lipid synthesis and hepatic fat stores in the postpartum period

In mothers who are nursing their infants, increased clearance of plasma metabolites into the mammary gland may reduce ectopic lipid in the liver. No study to date has investigated the role of lactation on liver lipid synthesis in humans, and we hypothesized that lactation would modify fatty acid and glucose handling to support liver metabolism in a manner synchronized with the demands of milk production. Lactating (n = 18) and formula-feeding women (n = 10) underwent metabolic testing at 6-week postpartum to determine whether lactation modified intrahepatic triacylglycerols (IHTGs), measured by proton magnetic resonance spectroscopy. Subjects ingested oral deuterated water to measure fractional de novo lipogenesis (DNL) in VLDL-TG during fasting and during an isotope-labeled clamp at an insulin infusion rate of 10 mU/m2/min. Compared with formula-feeding women, we found that lactating women exhibited lower plasma VLDL-TG concentrations, similar IHTG content and similar contribution of DNL to total VLDL-TG production. These findings suggest that lactation lowers plasma VLDL-TG concentrations for reasons that are unrelated to IHTG and DNL. Surprisingly, we determined that the rate of appearance of nonesterified fatty acids was not related to IHTG in either group, and the expected positive association between DNL and IHTG was only significant in formula-feeding women. Further, in lactating women only, the higher the prolactin concentration, the lower the IHTG, while greater DNL strongly associated with elevations in VLDL-TG. In conclusion, we suggest that future studies should investigate the role of lactation and prolactin in liver lipid secretion and metabolism.

Joint effect of multiple air pollutants on cardiometabolic health in normal-weight and obese adults: A novel insight into the role of circulating free fatty acids

The cardiometabolic effects of air pollution in the context of mixtures and the underlying mechanisms remain not fully understood. This study aims to investigate the joint effect of air pollutant mixtures on a broad range of cardiometabolic parameters, examine the susceptibility of obese individuals, and determine the role of circulating fatty acids. In this panel study, metabolically healthy normal-weight (MH-NW, n = 49) and obese (MHO, n = 39) adults completed three longitudinal visits (257 person-visits in total). Personal exposure levels of PM2.5, PM10, O3, NO2, SO2, CO and BC were estimated based on fixed-site monitoring data, time-activity logs and infiltration factor method. Blood pressure, glycemic homeostasis, lipid profiles, systematic inflammation and coagulation biomarkers were measured. Targeted metabolomics was used to quantify twenty-eight plasma free fatty acids (FFAs). Bayesian kernel machine regression models were applied to establish the exposure-response relationships and identify key pollutants. Significant joint effects of measured air pollutants on systematic inflammation and coagulation biomarkers were observed in the MHO group, instead of the MH-NW group. Lipid profiles showed the most significant changes in both groups and O3 contributed the most to the total effect. Specific FFA patterns were identified, and de novo lipogenesis (DNL)-related pattern was most closely related to blood lipid profiles. In particular, interaction analysis suggested that DNL-related FFA pattern augmented the effects of O3 on triglyceride (TG, Pinteraction = 0.040), high-density lipoprotein cholesterol (HDL-C, Pinteraction = 0.106) and TG/HDL-C (Pinteraction = 0.020) in the MHO group but not MH-NW group. This modification was further confirmed by interaction analysis with estimated activity of SCD1, a key enzyme in the DNL pathway. Therefore, despite being metabolically healthy, obese subjects have a higher cardiometabolic susceptibility to air pollution, especially O3, and the DNL pathway may represent an intrinsic driver of lipid susceptibility. This study provides new insights into the cardiometabolic susceptibility of obese individuals to air pollution.

Regulation of lipid droplet (LD) formation in hepatocytes via regulation of SREBP1c by non-coding RNAs.

IntroductionIncreased de novo lipogenesis (DNL) is one of the key factors contributing to fat accumulation and non-alcoholic fatty liver disease (NAFLD). Among the critical transcription factors (TFs) regulating DNL is mTOR and its downstream lipogenic TF, SREBP1c. In recent years, it has been established that non-coding RNAs (ncRNAs) play role in both biological processes and disease pathogenesis. Our group has previously characterized microRNAs that can target and regulate the expression of both mTOR and SREBP1c. Accordingly, this study aimed to broaden our understanding of the role of ncRNAs in regulating the mTOR/SREBP1c axis to elucidate the role of the non-coding transcriptome in DNL and lipid droplet (LD) formation. Hence, short ncRNA, miR-615-5p, and long non-coding RNA (lncRNA), H19, were chosen as they were previously proven to target mTOR by our group and in the published literature, respectively.MethodologyHuh-7 cells were treated with 800 μM oleic acid (OA) to promote LD formation. Transfection of miR-615-5p mimics or H19 over-expression vectors was performed, followed by the measurement of their downstream targets, mTOR and SREBP, on the mRNA level by quantitative real-time PCR (qRT-PCR), and on the protein level by Western blot. To determine the functional impact of miR-615-5p and H19 on LD formation and triglyceride (TG) accumulation, post-transfection LDs were stained, imaged, and characterized, and TGs were extracted and quantified.ResultsmiR-615-5p was able to reduce mTOR and SREBP1c significantly on both the mRNA and protein levels compared to control cells, while H19 caused a reduction of both targets on the protein level only. Both miR-615-5p and H19 were able to significantly reduce the LD count and total area, as well as TG levels compared to control cells.ConclusionTo conclude, this study shows, for the first time, the impact of miR-615-5p and H19 on the mTOR/SREBP1c axis, and thus, their functional impact on LDs and TG accumulation. These findings might pave the way for using ncRNAs as potential therapeutic targets in the management of fatty liver.

Association between de novo lipogenesis susceptibility genes and coronary artery disease

Background and aimsCoronary artery disease (CAD) is the principal cause of death in individuals with non-alcoholic fatty liver disease (NAFLD). The aim of this study was to use genetic epidemiology to study the association between de novo lipogenesis (DNL), one of the major pathways leading to NAFLD, and CAD risk. Methods and resultsDNL susceptibility genes were used as instruments and selected using three approaches: 1) genes that are associated with both high serum triglycerides and low sex hormone-binding globulin, both downstream consequences of DNL (unbiased approach), 2) genes that have a known role in DNL (biased approach), and 3) genes that have been associated with serum fatty acids, used as a proxy of DNL. Gene-CAD effect estimates were retrieved from the meta-analysis of CARDIoGRAM and the UK Biobank (∼76014 cases and ∼264785 controls). Effect estimates were clustered using a fixed-effects meta-analysis. Twenty-two DNL susceptibility genes were identified by the unbiased approach, nine genes by the biased approach and seven genes were associated with plasma fatty acids. Clustering of genes selected in the unbiased and biased approach showed a statistically significant association with CAD (OR:1.016, 95%CI:1.012; 1.020 and OR:1.013, 95%CI:1.007; 1.020, respectively), while clustering of fatty acid genes did not (OR:1.004, 95%CI:0.996–1.011). Subsequent exclusion of potential influential outliers did reveal a statistically significant association (OR:1.009, 95%CI:1.000; 1.018). ConclusionsDNL susceptibility genes are associated with an increased risk of CAD. These findings suggest that DNL may be involved in the pathogenesis of CAD and favor further development of strategies that target NAFLD through DNL.

Deficiency of peroxisomal NUDT7 stimulates de novo lipogenesis in hepatocytes

SummaryHere, we found that heterozygous null of peroxisomal Nudt7 (Nudt7+/−) induced the typical NAFLD features, i.e. increased levels of hepatic triglyceride (TG) and fatty acid (FA), infiltration of inflammatory cells, impaired glucose tolerance and insulin sensitivity, and stimulation of lipolysis from adipose tissue. Particularly, in Nudt7+/− hepatocytes, de novo lipogenesis (DNL) was significantly increased. Ingenuity pathway analysis (IPA) and KEGG pathway analysis of RNA sequencing data suggested the activation of PPAR signaling in the liver of Nudt7+/− mice. Moreover, accumulation of palmitic acid in Nudt7+/− hepatocyte increased the level of H3K4me3 on the promoters of PPARγ resulting in the activation of PPARγ and induced the DNL in the hepatocytes of Nudt7+/− mice. Moreover, we found that liraglutide significantly reduced typical NAFLD features induced by NUDT7 deficiency. Our data suggest that dysregulation of peroxisomal NUDT7 is responsible for upregulation of hepatic DNL by accumulation of palmitic acid and PPARγ activation.

Hepatocyte leukotriene B4 receptor 1 promotes NAFLD development in obesity.

NAFLD is the most prevalent chronic liver disease worldwide and has emerged as a serious public health issue with no approved treatment. The development of NAFLD is strongly associated with hepatic lipid content, and patients with NAFLD have significantly higher rates of hepatic de novo lipogenesis (DNL) than lean individuals. Leukotriene B4 (LTB4), a metabolite of arachidonic acid, is dramatically increased in obesity and plays important role in proinflammatory cytokine production and insulin resistance. But the role of liver LTB4/LTB4 receptor 1 (Ltb4r1) in lipid metabolism is unclear. Hepatocyte-specific knockout (HKO) of Ltb4r1 improved hepatic steatosis and systemic insulin resistance in both diet-induced and genetically induced obese mice. The mRNA level of key enzymes involved in DNL and fatty acid esterification decreased in Ltb4r1 HKO obese mice. LTB4/Ltb4r1 directly promoted lipogenesis in HepG2 cells and primary hepatocytes. Mechanically, LTB4/Ltb4r1 promoted lipogenesis by activating the cAMP-protein kinase A (PKA)-inositol-requiring enzyme 1α (IRE1α)-spliced X-box-binding protein 1 (XBP1s) axis in hepatocytes, which in turn promoted the expression of lipogenesis genes regulated by XBP1s. In addition, Ltb4r1 suppression through the Ltb4r1 inhibitor or lentivirus-short hairpin RNA delivery alleviated the fatty liver phenotype in obese mice. LTB4/Ltb4r1 promotes hepatocyte lipogenesis directly by activating PKA-IRE1α-XBP1s to promote lipogenic gene expression. Inhibition of hepatocyte Ltb4r1 improved hepatic steatosis and insulin resistance. Ltb4r1 is a potential therapeutic target for NAFLD.

Visualization and quantification of de novo lipogenesis using a FASN-2A-GLuc mouse model.

BackgroundDe novo lipogenesis (DNL) is a dynamic process that converts excess carbohydrates into fatty acids to maintain cellular homeostasis. Dysregulation of DNL is associated with diverse obesity-related diseases and many tumor types. Therefore, monitoring DNL in real-time with high sensitivity should be highly beneficial when screening therapeutic agents for their potential use as obesity treatments.MethodsA sequence coding for Gaussia luciferase (GLuc) preceded by a 2A peptide was inserted into the murine fatty acid synthase (FASN) genetic locus by homologous recombination to generate FASN-2A-GLuc mice. The luciferase mouse model was evaluated in conditions of physical and pharmacological stimuli by in vivo and ex vivo imaging.ResultsThe distribution of bioluminescence signals in different organs was identical to the FASN expression: high in white fat, brown fat, and the lungs. In addition, the bioluminescence signals accurately recapitulated the dynamic change of FASN in response to fasting and refeeding conditions. Moreover, with this murine reporter model, we also discovered that fatostatin, a synthetic inhibitor of sterol regulatory element-binding proteins, effectively inhibited DNL in multiple organs, especially in adipose tissues under a high-carbohydrate diet.ConclusionsOur FASN-2A-GLuc reporter mouse model proved to be a sensitive visualization tool for monitoring both systemic and organ-specific DNL in real time.

Physiopathology of nonalcoholic fatty liver disease: from diet to nutrigenomics.

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide and is strongly associated with metabolic disorders, such as obesity, type 2 diabetes mellitus, and metabolic syndrome, to the extent that a new definition of metabolic associated fatty liver disease has been proposed. Insulin resistance, worsened by a high-fat and high-carbohydrate diet, is the key to the physiopathology of hepatic steatosis. This is driven by several mechanisms that are mostly activated at a genetic level, such as de-novo lipogenesis and triglyceride synthesis. Therefore, many diet regimens have been studied, although significant controversies remain regarding their metabolic effects and long-term sustainability. In this review, we summarized the role and effects of the main macronutrients on the development of NAFLD and discussed the molecular mechanisms involved. We also discussed the importance of genetic polymorphisms, epigenetic alterations, and dysbiosis to determine if lifestyle modification and a specific dietary regimen could be an essential part of NAFLD treatment.