De Novo Lipogenesis Pathway Research Articles

Amelioration of fructose-induced hepatic lipid accumulation by vitamin D3 supplementation and high-intensity interval training in male Sprague‒Dawley rats

BackgroundIntrahepatic lipid accumulation (IHL), a hallmark of metabolic disorders, is closely associated with de novo lipogenesis (DNL). Notably, fructose feeding increased the DNL. Lifestyle modifications resulting from dietary changes and increased physical activity/exercise can decrease the IHL content. We examined the effects of vitamin D3 supplementation (VDS), high-intensity interval training (HIIT), and their combination on the transcription factors and enzymes of the DNL pathway in male Sprague‒Dawley rats fed a high-fructose diet (HFrD).MethodsForty male rats were assigned to 5 groups (n = 8): CS (the control group had a standard diet); CF (the control group had HFrD (10% (w/v) fructose solution in tap water)); and FT (HFrD + HIIT: 10 bouts of 4 min of high-intensity running, corresponding to 85–90% of the maximal speed with 2 min active rest periods of 50% maximal speed, 5 days per week); FD (HFrD + intervention of intraperitoneal injection of 10000 IU/kg/week VDS); FTD (HFrD + HIIT + VDS) that were maintained for 12 weeks. ELISA, the GOD-POD assay, folch, western blotting, and oil red O staining were used to determine insulin, fasting blood glucose (FBG), hepatic triglyceride (TG) and cholesterol levels; SREBP1c, ChREBP-β, ACC1, FASN, p-ACC1, AMPK, p-AMPK, and PKA protein expression; and IHL content, respectively.ResultsBoth HIIT and VDS led to significant increases in the levels of PKA, AMPK, p-AMPK, and p-ACC1, as well as significant decreases in the levels of SREBP1c, ChREBP-β, ACC1, FASN, insulin, FBG, liver TG, liver cholesterol, and IHL. HIIT exhibited superior efficacy over VDS in reducing ChREBP-β, ACC1, insulin, FBG, liver TG and cholesterol, as well as increasing p-ACC1 and PKA. Notably, the combined intervention of HIIT and VDS yielded the most substantial improvements across all the parameters.ConclusionsHFrD causes IHL accumulation and the onset of diabetes, whereas VDS and HIIT, along with their combined effects, prevent the consequences of HFrD.

Liver proteomics identifies a disconnect between proteins associated with de novo lipogenesis and triglyceride storage

De novo lipogenesis (DNL) has been implicated in the development and progression of liver steatosis. Hepatic DNL is strongly influenced by dietary macronutrient composition with diets high in carbohydrate increasing DNL and while diets high in fat decrease DNL. The enzymes in the core DNL pathway have been well characterised, however less is known about other liver proteins that play accessory or regulatory roles. In the current study, we associate measured rates of hepatic DNL and fat content with liver proteomic analysis in mice to identify known and unknown proteins that may have a role in DNL. Male mice were fed either a standard chow diet, a semi-purified high starch or high fat diet. Both semi-purified diets resulted in increased body weight, fat mass and liver triglyceride content compared to chow controls and hepatic DNL was increased in the high starch and decreased in high fat fed mice. Proteomic analysis identified novel proteins associated with DNL that are involved in taurine metabolism, suggesting a link between these pathways. There was no relationship between proteins that associated with DNL and those associated with liver triglyceride content. Further analysis identified proteins that are differentially regulated when comparing a non-purified chow diet to either of the semi-purified diets which provide a set of proteins that are influenced by dietary complexity. Finally, we compared the liver proteome between 4- and 30-week diet-fed mice and found remarkable similarity suggesting metabolic remodelling of the liver occurs rapidly in response to differing dietary components.

Mixed exposure to haloacetaldehyde disinfection by-products exacerbates lipid aggregation in the liver of mice

Haloacetaldehyde disinfection by-products (HAL-DBPs) are among the top three unregulated DBPs found in drinking water. The cytotoxicity and genotoxicity of HALs are much higher than that of the regulated trihalomethanes and haloacetic acids. Previous studies have mainly focused on the toxic effects of single HAL, with few examining the toxic effects of mixed exposures to HALs. The study aimed to observe the effects of mixed exposures of 1∼1000X the realistic level of HALs on the hepatotoxicity and lipid metabolism of C57BL/6J mice, based on the component and concentration of HALs detected in the finished water of Shanghai. Exposure to realistic levels of HALs led to a significant increase in phosphorated acetyl CoA carboxylase 1 (p-ACC1) in the hepatic de novo lipogenesis (DNL) pathway. Additionally, exposure to 100X realistic levels of HALs resulted in significant alterations to key enzymes of DNL pathway, including ACC1, fatty acid synthase (FAS), and diacylglycerol acyltransferase 2 (DGAT2), as well as key proteins of lipid disposal such as carnitine palmitoyltransferase 1 (CPT-1) and peroxisome proliferator activated receptor α (PPARα). Exposure to 1000X realistic levels of HALs significantly increased hepatic and serum triglyceride levels, as well as total cholesterol, low-density lipoprotein, alanine aminotransferase, aspartate transaminase, alkaline phosphatase, and lactate dehydrogenase levels, significantly decreased high-density lipoprotein. Meanwhile, histopathological analysis demonstrated that HALs exacerbated tissue vacuolization and inflammatory cell infiltration in mice livers, which showed the typical phenotypes of non-alcoholic fatty liver disease (NAFLD). These results suggested that the HALs mixture is a critical risk factor for NAFLD and is significantly highly toxic to C57BL/6J mice.

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.

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.

Omega-3 fatty acids and metabolic partitioning of fatty acids within the liver in the context of nonalcoholic fatty liver disease.

Nonalcoholic fatty liver disease (NAFLD) is now the most prevalent form of liver disease globally, affecting about 25% of the world's adult population. It is more common in those living with obesity, where it may affect as many as 80% of individuals. The aim of this article is to describe recent human studies evaluating the influence of omega-3 fatty acids on de novo lipogenesis (DNL) and hepatic fatty acid partitioning between incorporation into triacylglycerols (TAGs) and β-oxidation, to discuss the relevance of these effects in the context of NAFLD, and to provide an overview of the mechanisms that might be involved. The omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) decrease hepatic DNL and partition fatty acids away from TAG synthesis and toward β-oxidation. EPA and DHA affect multiple hepatic transcription factors resulting in down-regulation of the DNL pathway and upregulation of β-oxidation. The net result is decreased accumulation of hepatic TAG and lowering of circulating TAG concentrations. Human trials demonstrate that EPA and DHA can decrease liver fat in patients with NAFLD. Increased intake of EPA and DHA may reduce the likelihood of hepatic TAG accumulation and could be used to reduce liver fat in patients with NAFLD.

Molecular Basis for Regulation of Mammalian Fatty Acid Synthase

De novo lipogenesis (DNL) is an essential metabolic process that converts excess cellular glucose to fatty acids. Fatty Acid Synthase (FASN) is a key enzyme in the DNL pathway and has shown promising pre‐clinical results as a therapeutic target in a variety of metabolic diseases, including cancer, non‐alcoholic fatty liver disease (NAFLD), and most recently COVID‐19. Mammalian FASN is a large multifunctional enzyme with 6 catalytic domains and a flexibly tethered acyl carrier protein (ACP). The ACP shuttles covalently linked intermediates between catalytic domains to facilitate palmitate synthesis. Previous negative stain electron microscopy data has shown that mammalian FASN is a dynamic enzyme that adopts multiple conformations in solution, but the role of these conformational dynamics in the mechanism of FASN is yet to be determined. To understand how the conformational dynamics of mammalian FASN contribute to the overall mechanism and its’ regulation, we have generated multiple constructs and characterized their enzymatic activity using diverse biochemical assays. Additionally, we have made progress towards understanding the enzyme dynamics using Hydrogen‐Deuterium Exchange Mass Spectrometry (HDX‐MS). We are actively pursuing structural studies to implement an integrative approach towards advancing our understanding of the complex mechanism of mammalian FASN.

Epigallocatechin gallate triggers apoptosis by suppressing de novo lipogenesis in colorectal carcinoma cells.

The de novo lipogenesis (DNL) pathway has been identified as a regulator of cancer progression and aggressiveness. Downregulation of key lipogenesis enzymes has been shown to activate apoptosis in cancerous cells. Epigallocatechin gallate (EGCG) inhibits cancer cell proliferation without causing cytotoxicity in healthy cells. The present study aimed to investigate the effects of EGCG on the promotion of apoptosis associated with the DNL pathway inhibition in cancer cells, both in vitro and in vivo. We observed that two colorectal cancer cell lines (HCT116 and HT‐29) had a higher cytotoxic response to EGCG treatment than hepatocellular carcinoma cells, including HepG2 and HuH‐7. EGCG treatment decreased cell viability and increased mitochondrial damage‐triggered apoptosis in both HCT116 and HT‐29 cancer cells. Additionally, we treated mice transplanted with HCT116 cells with 30 or 50 mg·kg−1 EGCG for 7 days to evaluate the apoptotic effects of EGCG treatment in a xenograft mouse model of cancer. We observed a decrease in intracellular fatty acid levels, which suggested that EGCG‐induced apoptosis was associated with a decrease in fatty acid levels in cancer. Suppression of ATP synthesis by EGCG indicated that cell death induction in cancer cells could be mediated by shared components of the DNL and energy metabolism pathways. In addition, EGCG‐induced apoptosis suppressed the expression of the phosphorylation protein kinase B and extracellular signal‐regulated kinase 1/2 signaling proteins in tumors from xenografted mice. Cytotoxic effects in unaffected organs and tissues of the mouse xenograft model were absent upon EGCG treatment.

Quercetin Reduces Lipid Accumulation in a Cell Model of NAFLD by Inhibiting De Novo Fatty Acid Synthesis through the Acetyl-CoA Carboxylase 1/AMPK/PP2A Axis.

Dysregulation of de novo lipogenesis (DNL) has recently gained strong attention as being one of the critical factors that contribute to the assessment of non-alcoholic fatty liver disease (NAFLD). NAFLD is often diagnosed in patients with dyslipidemias and type 2 diabetes; thus, an interesting correlation can be deduced between high hematic free fatty acids and glucose excess in the DNL dysregulation. In the present study, we report that, in a cellular model of NAFLD, the coexistence of elevated glucose and FFA conditions caused the highest cellular lipid accumulation. Deepening the molecular mechanisms of the DNL dysregulation—RT-qPCR and immunoblot analysis demonstrated increased expression of mitochondrial citrate carrier (CiC), cytosolic acetyl-CoA carboxylase 1 (ACACA), and diacylglycerol acyltransferase 2 (DGAT2) involved in fatty acids and triglycerides synthesis, respectively. XBP-1, an endoplasmic reticulum stress marker, and SREBP-1 were the transcription factors connected to the DNL activation. Quercetin (Que), a flavonoid with strong antioxidant properties, and noticeably reduced the lipid accumulation and the expression of SREBP-1 and XBP-1, as well as of their lipogenic gene targets in steatotic cells. The anti-lipogenic action of Que mainly occurs through a strong phosphorylation of ACACA, which catalyzes the committing step in the DNL pathway. The high level of ACACA phosphorylation in Que-treated cells was explained by the intervention of AMPK together with the reduction of enzymatic activity of PP2A phosphatase. Overall, our findings highlight a direct anti-lipogenic effect of Que exerted through inhibition of the DNL pathway by acting on ACACA/AMPK/PP2A axis; thus, suggesting this flavonoid as a promising molecule for the NAFLD treatment.

Associations of plasma glycerophospholipid profile with modifiable lifestyles and incident diabetes in middle-aged and older Chinese.

Glycerophospholipid (GPL) perturbance was linked to the pathogenesis of diabetes in animal studies but prospective studies in humans are rare, particularly in Asians. We aimed to investigate the associations between plasma GPLs and incident diabetes and to explore effects of lifestyle on the associations in a Chinese population. The study included 1877 community-dwelling Chinese individuals aged 50-70years (751 men and 1126 women), free of diabetes at baseline and followed for 6years. A total of 160 GPL species were quantified in plasma at baseline by using high-throughput targeted lipidomics. Log-Poisson regression was used to assess the associations between GPLs and incidence of diabetes. Over the 6years of follow-up, 499 participants (26.6%) developed diabetes. After multivariable adjustment, eight GPLs were positively associated with incident diabetes (RRper SD 1.13-1.25; all false-discovery rate [FDR]-corrected p < 0.05), including five novel GLPs, namely phosphatidylcholines (PCs; 16:0/18:1, 18:0/16:1, 18:1/20:3), lysophosphatidylcholine (LPC; 20:3) and phosphatidylethanolamine (PE; 16:0/16:1), and three reported GPLs (PCs 16:0/16:1, 16:0/20:3 and 18:0/20:3). In network analysis, a PC-containing module was positively associated with incident diabetes (RRper SD 1.16 [95% CI 1.06, 1.26]; FDR-corrected p< 0.05). Notably, three of the diabetes-associated PCs (16:0/16:1, 16:0/18:1 and 18:0/16:1) and PE (16:0/16:1) were associated not only with fatty acids in the de novo lipogenesis (DNL) pathway, especially 16:1n-7 (Spearman correlation coefficients = 0.35-0.62, p< 0.001), but also with an unhealthy dietary pattern high in refined grains and low in fish, dairy and soy products (|factor loadings| ≥0.2). When stratified by physical activity levels, the associations of the eight GPLs and the PC module with incident diabetes were stronger in participants with lower physical activity (RRper SD 1.24-1.49, FDR-corrected p< 0.05) than in those with the median and higher physical activity levels (RRper SD 1.03-1.12, FDR-corrected p ≥ 0.05; FDR-corrected pinteraction < 0.05). Eight GPLs, especially PCs associated with the DNL pathway, were positively associated with incident diabetes in a cohort of Chinese men and women. The associations were most prominent in participants with a low level of physical activity.

Identifying Long Noncoding RNA Dependencies Using CRISPR Interference (CRISPRi)-Based Platform in Multiple Myeloma

Identifying Long Noncoding RNA Dependencies Using CRISPR Interference (CRISPRi)-Based Platform in Multiple Myeloma

OAB-009: Genome-wide CRISPR interference screen identifies RNA Regulator of Lipogenesis (RROL) as a leading LncRNA dependency in Multiple Myeloma

OAB-009: Genome-wide CRISPR interference screen identifies RNA Regulator of Lipogenesis (RROL) as a leading LncRNA dependency in Multiple Myeloma

Inhibition of Acetyl-CoA Carboxylase Causes Malformations in Rats and Rabbits: Comparison of Mammalian Findings and Alternative Assays.

Acetyl-CoA carboxylase (ACC) is an enzyme within the de novo lipogenesis (DNL) pathway and plays a role in regulating lipid metabolism. Pharmacologic ACC inhibition has been an area of interest for multiple potential indications including oncology, acne vulgaris, metabolic diseases such as type 2 diabetes mellitus, and nonalcoholic fatty liver disease/nonalcoholic steatohepatitis. A critical role for ACC in de novo synthesis of long-chain fatty acids during fetal development has been demonstrated in studies in mice lacking Acc1, where the absence of Acc1 results in early embryonic lethality. Following positive predictions of developmental toxicity in the alternative in vitro assays (positive in murine embryonic stem cell [mESC] assay and rat whole embryo culture, but negative in zebrafish), developmental toxicity (growth retardation and dysmorphogenesis associated with disrupted midline fusion) was observed with the oral administration of the dual ACC1 and 2 inhibitors, PF-05175157, in Sprague Dawley rats and New Zealand White rabbits. The results of these studies are presented here to make comparisons across the assays, as well as mechanistic insights from the mESC assay demonstrating high ACC expression in the mESC and that ACC-induced developmental toxicity can be rescued with palmitic acid providing supportive evidence for DNL pathway inhibition as the underlying mechanism. Ultimately, while the battery of alternative approaches and weight-of-evidence case were useful for hazard identification, the embryo-fetal development studies were necessary to inform the risk assessment on the adverse fetal response, as malformations and/or embryo-fetal lethality were limited to doses that caused near-complete inhibition of DNL.

RNA Regulator of Lipogenesis (RROL) Is a Novel Lncrna Mediating Protein-Protein Interaction at Gene Regulatory Loci Driving Lipogenic Programs in Multiple Myeloma

Long noncoding RNA (lncRNAs) are key epigenetic factors that drive the origin and progression of human cancers via mechanisms that are largely unknown. We have previuosly reported the clinical significance of a lncRNA signature in multiple myeloma (MM) as independent risk predictor for clinical outcome; and recently identified a lncRNA RROL (RNA Regulator of Lipogenesis) with impact on MM cell proliferation. Here we describe a unique regulatory function for RROL in the control of gene networks involved in the de novo lipogenesis (DNL) pathway, ultimately impacting MM cell growth and survival. Based on growth and survival impact of RROL depletion, we performed integrated transcriptomic analysis of RNA-seq data after RROL depletion in MM cell lines and CD138+ patient MM cells, and identified a set of significantly modulated metabolic genes including the acetyl Co-A Carboxylase 1 (ACC1) gene, encoding a rate-limiting enzyme of the DNL pathway. This metabolic pathway converts nutrients into fatty acids serving for energy storage or biosynthesis of membranes and signaling molecules. Consistent with the transcriptional control of ACC1, we have observed that RROL inhibition in cell lines and primary MM cells significantly decreased the incorporation of C14-radiolabeled glucose into de novo synthesized lipids. Importantly, supplementation with exogenous palmitate, the main downstream product of DNL pathway, rescued the growth inhibitory effect of RROL depletion on MM cells, further confirming the importance of the DNL pathway in the oncogenic activity of RROL in MM. To understand the molecular mechanism through which RROL regulates ACC1 expression and its metabolic axis, we evaluated the RROL interactome in MM cells. RNA-Protein Pull Down (RPPD) and in vivo RNA yeast three-hybrid (Y3H) assays led to the identification of MYC as relevant direct partner of RROL. These results were further validated by qRT-PCR analysis of MYC-bound RNA obtained through RNA immunoprecipitation (RIP) assay. Using experimental model of conditional MYC KD (P493-6), we found that RROL exerts regulatory activity on ACC1 only in the presence of MYC. Mapping of MYC genomic occupancy by ChIP-seq and gene expression after MYC KD in MM cells revealed that ACC1 is a direct transcriptional target of MYC in cells expressing RROL. These data indicate that RROLand MYC cooperate in the transcriptional control of ACC1. Moreover, we found that RROL itself is transcriptionally regulated by MYC, suggesting the existence of a feed-forward regulatory loop in which MYC enhances the expression of RROL that, in turn, drives MYC transcriptional activity to ACC1. We hypothesized that RROL may shape the protein interacting network of MYC to confer specificity for ACC1 promoter. To this end, we performed mass spectrometry analysis of MYC interactome in three MM cell lines in the presence or in the absence of RROL and identified the transcriptional modulator WDR82 as RROL-dependent MYC partner. Interestingly, WDR82 directly interacts with RROL as assessed in the RPPD and RNA Y3H assays, and transcriptionally regulates ACC1 in RROL-dependent manner. These data indicate that RROL catalyzes the interaction of MYC with the transcriptional modulator WDR82 to form a transcriptional ternary complex regulating ACC1 expression. To therapeutically antagonize the RROL lipogenic signaling we have pre-clinically tested small molecule inhibitors of ACC1 (ACC1i). We have observed significant anti-MM activity of ACC1i in vitro in a large panel of MM cell lines and primary MM cells from patients; and in vivo in mouse models of human MM including the localized subcutaneous model and the disseminated model that establish a more aggressive systemic disease. Importantly, we have now developed clinically applicable ASOs and small molecule-like compounds to directly target RROL in MM cells. These studies are ongoing and will be presented. In conclusion, we here report a unique regulatory function of a novel lncRNA supporting MM cell growth via its control of the lipogenic metabolic axis. The availability of oral inhibitors of ACC1 as well as the ongoing development of RROL inhibitors may allow clinical application of this unique targeted therapy in MM. Disclosures Fulciniti: NIH: Research Funding. Chauhan:Oncopeptide AB: Consultancy; consultant to Stemline Therapeutics, Inc., and Equity owner in C4 Therapeutics.: Consultancy, Other: Equity owner in C4 Therapeutics.. Anderson:Celgene: Membership on an entity's Board of Directors or advisory committees; Millenium-Takeda: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Sanofi-Aventis: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Oncopep and C4 Therapeutics.: Other: Scientific Founder of Oncopep and C4 Therapeutics.. Munshi:Takeda: Consultancy; Karyopharm: Consultancy; AbbVie: Consultancy; Amgen: Consultancy; Legend: Consultancy; Adaptive: Consultancy; Janssen: Consultancy; C4: Current equity holder in private company; OncoPep: Consultancy, Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees, Patents &amp; Royalties; BMS: Consultancy.

Serial Plasma Phospholipid Fatty Acids in the De Novo Lipogenesis Pathway and Total Mortality, Cause-Specific Mortality, and Cardiovascular Diseases in the Cardiovascular Health Study.

BackgroundSynthesized fatty acids (FAs) from de novo lipogenesis may affect cardiometabolic health, but longitudinal associations between serially measured de novo lipogenesis–related fatty acid biomarkers and mortality or cardiovascular disease (CVD) are not well established.Methods and ResultsWe investigated longitudinal associations between de novo lipogenesis–related fatty acids with all‐cause mortality, cause‐specific mortality, and incident CVD among 3869 older US adults, mean (SD) age 75 (5) years and free of prevalent CVD at baseline. Levels of plasma phospholipid palmitic (16:0), palmitoleic (16:1n‐7), stearic (18:0), oleic acid (18:1n‐9), and other risk factors were serially measured at baseline, 6 years, and 13 years. All‐cause mortality, cause‐specific mortality, and incident fatal and nonfatal CVD were centrally adjudicated. Risk was assessed in multivariable‐adjusted Cox models with time‐varying FAs and covariates. During 13 years, median follow‐up (maximum 22.4 years), participants experienced 3227 deaths (1131 CVD, 2096 non‐CVD) and 1753 incident CVD events. After multivariable adjustment, higher cumulative levels of 16:0, 16:1n‐7, and 18:1n‐9 were associated with higher all‐cause mortality, with extreme‐quintile hazard ratios (95% CIs) of 1.35 (1.17–1.56), 1.40 (1.21–1.62), and 1.56 (1.35–1.80), respectively, whereas higher levels of 18:0 were associated with lower mortality (hazard ratio=0.76; 95% CI=0.66–0.88). Associations were generally similar for CVD mortality versus non‐CVD mortality, as well as total incident CVD. Changes in levels of 16:0 were positively, and 18:0 inversely, associated with all‐cause mortality (hazard ratio=1.23, 95% CI=1.08–1.41; and hazard ratio=0.78, 95% CI=0.68–0.90).ConclusionsHigher long‐term levels of 16:0, 16:1n‐7, and 18:1n‐9 and changes in 16:0 were positively, whereas long‐term levels and changes in 18:0 were inversely, associated with all‐cause mortality in older adults.

De Novo Lipogenesis as a Source of Second Messengers in Adipocytes.

Obesity is a major risk factor for type 2 diabetes. Although adipose tissue allows storage of excess calories in periods of overnutrition, in obesity, adipose tissue metabolism becomes dysregulated and can promote metabolic diseases. This review discusses recent advances in understandings how adipocyte metabolism impacts metabolic homeostasis. The ability of adipocytes to synthesize lipids from glucose is a marker of metabolic fitness, e.g., low de novo lipogenesis (DNL) in adipocytes correlates with insulin resistance in obesity. Adipocyte DNL may promote synthesis of special "insulin sensitizing" signaling lipids that act hormonally. However, each metabolic intermediate in the DNL pathway (i.e., citrate, acetyl-CoA, malonyl-CoA, and palmitate) also has second messenger functions. Mounting evidence suggests these signaling functions may also be important for maintaining healthy adipocytes. While adipocyte DNL contributes to lipid storage, lipid precursors may have additional second messenger functions critical for maintaining adipocyte health, and thus systemic metabolic homeostasis.

Effects of temperature shifts on life parameters and expression of fatty acid synthesis and heat shock protein genes in temperate and Antarctic copepods Tigriopus japonicus and Tigriopus kingsejongensis

Global warming, increase of the atmospheric temperature leading to changes in climate, is a growing environmental concern for all organisms including marine organisms, and many efforts have been made to reveal the potential adverse effects on the systematics of aquatic organisms in response to the temperature changes. To examine the effects of temperature shifts on copepods in temperate and polar regions, we compared the life parameters and gene expression profiles of the de novo lipogenesis (DNL) pathway and heat shock protein (hsp) genes in the temperate copepod Tigriopus japonicus (T. japonicus) and the Antarctic copepod Tigriopus kingsejongensis (T. kingsejongensis). The median lethal temperature (LT50) and no observed effect level (NOEL) in the temperate copepod T. japonicus were determined to be 35.3 and 32 °C, respectively, in response to a temperature increase of 2 °C a day. In the Antarctic copepod T. kingsejongensis, the LT50 and NOEL were determined to be 24.8 and 12 °C, respectively. In addition, delayed developmental time and impaired fecundity were observed (P < 0.05) in response to temperature changes in T. japonicus. T. japonicus DNL pathway genes were down-regulated in response to high temperature, whereas T. kingsejongensis DNL pathway genes showed up-regulation in response to high temperature, indicating that these two Tigriopus species have different modes of action in response to temperature shifts. In both copepods, transcription of heat shock proteins (hsps) was mostly up-regulated in response to temperature shifts, but it showed moderate expression at 15 °C for T. japonicus and 4 °C for T. kingsejongensis. These findings indicate temperature shift-mediated species-specific modulations of the DNL pathway and hsps gene expression, leading to alteration of lipid synthesis and chaperoning with deleterious effects on the life parameters of these two copepods.

Suppressed de novo lipogenesis by plasma membrane citrate transporter inhibitor promotes apoptosis in HepG2 cells.

Suppression of the expression or activities of enzymes that are involved in the synthesis of de novo lipogenesis (DNL) in cancer cells triggers cell death via apoptosis. The plasma membrane citrate transporter (PMCT) is the initial step that translocates citrate from blood circulation into the cytoplasm for de novo long‐chain fatty acids synthesis. This study investigated the antitumor effect of the PMCT inhibitor (PMCTi) in inducing apoptosis by inhibiting the DNL pathway in HepG2 cells. The present findings showed that PMCTi reduced cell viability and enhanced apoptosis through decreased intracellular citrate levels, which consequently caused inhibition of fatty acid and triacylglycerol productions. Thus, as a result of the reduction in fatty acid synthesis, the activity of carnitine palmitoyl transferase‐1 (CPT‐1) was suppressed. Decreased CPT‐1 activity also facilitated the disruption of mitochondrial membrane potential (ΔΨm) leading to stimulation of apoptosis. Surprisingly, primary human hepatocytes were not affected by PMCTi. Increased caspase‐8 activity as a consequence of reduction in fatty acid synthesis was also found to cause disruption of ΔΨm. In addition, apoptosis induction by PMCTi was associated with an enhanced reactive oxygen species generation. Taken together, we suggest that inhibition of the DNL pathway following reduction in citrate levels is an important regulator of apoptosis in HepG2 cells via suppression of CPT‐1 activity. Thus, targeting the DNL pathway mediating CPT‐1 activity by PMCTi may be a selective potential anticancer therapy.

Effects of environmental stressors on lipid metabolism in aquatic invertebrates

Lipid metabolism is crucial for the survival and propagation of the species, since lipids are an essential cellular component across animal taxa for maintaining homeostasis in the presence of environmental stressors. This review aims to summarize information on the lipid metabolism under environmental stressors in aquatic invertebrates. Fatty acid synthesis from glucose via de novo lipogenesis (DNL) pathway is mostly well-conserved across animal taxa. The structure of free fatty acid (FFA) from both dietary and DNL pathway could be transformed by elongase and desaturase. In addition, FFA can be stored in lipid droplet as triacylglycerol, upon attachment to glycerol. However, due to the limited information on both gene and lipid composition, in-depth studies on the structural modification of FFA and their storage conformation are required. Despite previously validated evidences on the disturbance of the normal life cycle and lipid homeostasis by the environmental stressors (e.g., obesogens, salinity, temperature, pCO2, and nutrients) in the aquatic invertebrates, the mechanism behind these effects are still poorly understood. To overcome this limitation, omics approaches such as transcriptomic and proteomic analyses have been used, but there are still gaps in our knowledge on aquatic invertebrates as well as the lipidome. This paper provides a deeper understanding of lipid metabolism in aquatic invertebrates.

Epistructured catechins, EGCG and EC facilitate apoptosis induction through targeting de novo lipogenesis pathway in HepG2 cells

BackgroundAbnormally high expression of the mammalian de novo lipogenesis (DNL) pathway in various cancer cells promotes cell over-proliferation and resistance to apoptosis. Inhibition of key enzymes in the DNL pathway, namely, ATP citrate lyase, acetyl-CoA carboxylase, and fatty acid synthase (FASN) can increase apoptosis without cytotoxicity to non-cancerous cells, leading to the search for and presentation of novel selective and powerful targets for cancer therapy. Previous studies reported that epistructured catechins, epigallocatechin gallate (EGCG) and epicatechin (EC) exhibit different mechanisms regarding a strong inducer of apoptosis in various cancer cell lines. Thus, the current study investigated the growth inhibitory effect of EGCG and EC, on the enzyme expression and activity of the DNL pathway, which leads to the prominent activity of carnitine palmitoyl transferase-1 (CPT-1) mediating apoptosis in HepG2 cells.MethodsThe cytotoxicity on HepG2 cells of EGCG and EC was determined by MTT assay. Cell death caused by apoptosis, the dissipation of mitochondrial membrane potential (MMP), and cell cycle arrest were then detected by flow cytometry. We further investigated the decrease of fatty acid levels associated with DNL retardation, followed by evaluation of DNL protein expression. Then, the negative inhibitory effect of depleted fatty acid synthesis on malonyl-CoA synthesis followed by regulating of CPT-1 activity was investigated. Thereafter, we inspected the enhanced reactive oxygen species (ROS) generation, which is recognized as one of the causes of apoptosis in HepG2 cells.ResultsWe found that EGCG and EC decreased cancer cell viability by increasing apoptosis as well as causing cell cycle arrest in HepG2 cells. Apoptosis was associated with MMP dissipation. Herein, EGCG and EC inhibited the expression of FASN enzymes contributing to decreasing fatty acid levels. Notably, this decrease consequently showed a suppressing effect on the CPT-1 activity. We suggest that epistructured catechin-induced apoptosis targets CPT-1 activity suppression mediated through diminishing the DNL pathway in HepG2 cells. In addition, increased ROS production was found after treatment with EGCG and EC, indicating oxidative stress mechanism-induced apoptosis. The strong apoptotic effect of EGCG and EC was specifically absent in primary human hepatocytes.ConclusionOur supportive evidence confirms potential alternative cancer treatments by EGCG and EC that selectively target the DNL pathway.