VLDL hydrolysis by LPL activates PPAR-alpha through generation of unbound fatty acids

VLDL receptor gene therapy for reducing atherogenic lipoproteins

Over the past 40 years, there has been considerable research into the management and treatment of atherogenic lipid disorders. Although the majority of treatments and management strategies for cardiovascular disease (CVD) center around targeting low-density lipoprotein cholesterol (LDL-C), there is mounting evidence for the residual CVD risk attributed to high triglyceride (TG) and lipoprotein(a) (Lp(a)) levels despite the presence of lowered LDL-C levels. Among the biological mechanisms for clearing TG-rich lipoproteins, the VLDL receptor (VLDLR) plays a key role in the trafficking and metabolism of lipoprotein particles in multiple tissues, but it is not ordinarily expressed in the liver. Since VLDLR is capable of binding and internalizing apoE-containing TG-rich lipoproteins as well as Lp(a), hepatic VLDLR expression has the potential for promoting clearance of these atherogenic particles from the circulation and managing the residual CVD risk not addressed by current lipid lowering therapies. This review provides an overview of VLDLR function and the potential for developing a genetic medicine based on liver-targeted VLDLR gene expression.

Ewe early gestation supplementation with eicosapentaenoic and docosahexaenoic acids affects the liver, muscle, and adipose tissue fatty acid profile and liver mRNA expression in the offspring

Our objectives were to assess the effects of eicosapentaenoic (EPA) and docosahexaenoic acids (DHA) supplementation to pregnant ewes during the first third of gestation on their offspring's liver, adipose, and muscle tissues fatty acid (FA) profile and liver mRNA expression after a finishing period receiving diets with different FA profiles. Twenty-four post-weaning lambs, blocked by sex and body weight, were used in a 2 × 2 factorial arrangement of treatments. The first factor was dam supplementation (DS) in the first third of gestation with 1.61% of Ca salts of palm fatty acid distillate (PFAD) or Ca salts enriched with EPA-DHA. Ewes were exposed to rams with marking paint harnesses during the breeding. Ewes started DS at the day of mating, considered day 1 of conception. Twenty-eight days after mating, ultrasonography was used to confirm pregnancy, and nonpregnant ewes were removed from the groups. After weaning, the offspring lambs were supplemented (LS, second main factor) with two different FA sources (1.48% of PFAD or 1.48% of EPA-DHA) during the growing and fattening phase. Lambs were fed the LS diet for 56 d and sent to slaughter, where the liver, muscle, and adipose tissue samples were collected for FA analysis. Liver samples were collected for relative mRNA expression for genes associated with FA transport and metabolism. The data were analyzed as a mixed model in SAS (9.4). In the liver, the amount of C20:5 and C22:6 (P < 0.01) increased in lambs with LS-EPA-DHA, while some C18:1 cis FA isomers were greater in the lambs from DS-PFAD. In muscle, amounts of C22:1, C20:5, and C22:5 increased (P < 0.05) in lambs born from DS-EPA-DHA. The adipose tissue amounts of C20:5, C22:5, and C22:6 were greater (P < 0.01) in lambs from LS-EPA-DHA. Interactions (DS × LS; P < 0.05) were observed for DNMT3β, FABP-1, FABP-5, SCD, and SREBP-1; having greater mRNA expression in liver tissue of LS-EPA-DHA, DS-PFAD and LS-PFAD, DS-EPA-DHA lambs compared with the lambs in the other two treatments. Liver ELOVL2 mRNA relative expression (P < 0.03) was greater in the offspring of DS-PFAD. Relative mRNA expression (P < 0.05) of GLUT1, IGF-1, LPL, and PPARγ increased in the liver from LS-EPA-DHA lambs. Dam supplementation during early gestation using with different FA sources changed the lipid FA profile in MT, LT, and SAT during the finishing period depending on the tissue and type of FA source administered during the growing phase.

PPARα at the crossroad of metabolic-immune regulation in cancer

Rewiring metabolism to sustain cell growth, division, and survival is the most prominent feature of cancer cells. In particular, dysregulated lipid metabolism in cancer has received accumulating interest, since lipid molecules serve as cell membrane structure components, secondary signaling messengers, and energy sources. Given the critical role of immune cells in host defense against cancer, recent studies have revealed that immune cells compete for nutrients with cancer cells in the tumor microenvironment and accordingly develop adaptive metabolic strategies for survival at the expense of compromised immune functions. Among these strategies, lipid metabolism reprogramming toward fatty acid oxidation is closely related to the immunosuppressive phenotype of tumor-infiltrated immune cells, including macrophages and dendritic cells. Therefore, it is important to understand the lipid-mediated crosstalk between cancer cells and immune cells in the tumor microenvironment. Peroxisome proliferator-activated receptors (PPARs) consist of a nuclear receptor family for lipid sensing, and one of the family members PPARα is responsible for fatty acid oxidation, energy homeostasis, and regulation of immune cell functions. In this review, we discuss the emerging role of PPARα-associated metabolic-immune regulation in tumor-infiltrated immune cells, and key metabolic events and pathways involved, as well as their influences on antitumor immunity.

Emerging Evidence of Pathological Roles of Very-Low-Density Lipoprotein (VLDL)

Embraced with apolipoproteins (Apo) B and Apo E, triglyceride-enriched very-low-density lipoprotein (VLDL) is secreted by the liver into circulation, mainly during post-meal hours. Here, we present a brief review of the physiological role of VLDL and a systemic review of the emerging evidence supporting its pathological roles. VLDL promotes atherosclerosis in metabolic syndrome (MetS). VLDL isolated from subjects with MetS exhibits cytotoxicity to atrial myocytes, induces atrial myopathy, and promotes vulnerability to atrial fibrillation. VLDL levels are affected by a number of endocrinological disorders and can be increased by therapeutic supplementation with cortisol, growth hormone, progesterone, and estrogen. VLDL promotes aldosterone secretion, which contributes to hypertension. VLDL induces neuroinflammation, leading to cognitive dysfunction. VLDL levels are also correlated with chronic kidney disease, autoimmune disorders, and some dermatological diseases. The extra-hepatic secretion of VLDL derived from intestinal dysbiosis is suggested to be harmful. Emerging evidence suggests disturbed VLDL metabolism in sleep disorders and in cancer development and progression. In addition to VLDL, the VLDL receptor (VLDLR) may affect both VLDL metabolism and carcinogenesis. Overall, emerging evidence supports the pathological roles of VLDL in multi-organ diseases. To better understand the fundamental mechanisms of how VLDL promotes disease development, elucidation of the quality control of VLDL and of the regulation and signaling of VLDLR should be indispensable. With this, successful VLDL-targeted therapies can be discovered in the future.

Characterization of lipoprotein lipase storage vesicles in 3T3-L1 adipocytes

Lipoprotein lipase (LPL) is a secreted triglyceride lipase involved in the clearance of very-low-density lipoproteins and chylomicrons from circulation. LPL is expressed primarily in adipose and muscle tissues and transported to the capillary lumen. LPL secretion is regulated by insulin in adipose tissue; however, few studies have examined the regulatory and trafficking steps involved in secretion. Here, we describe the intracellular localization and insulin-dependent trafficking of LPL in 3T3-L1 adipocytes. We compared LPL trafficking to the better characterized trafficking pathways taken by leptin and GLUT4 (also known as SLC2A4). We show that the LPL trafficking pathway shares some characteristics of these other pathways, but that LPL subcellular localization and trafficking are distinct from those of GLUT4 and leptin. LPL secretion occurs slowly in response to insulin and rapidly in response to the Ca2+ ionophore ionomycin. This regulated trafficking is dependent on Golgi protein kinase D and the ADP-ribosylation factor GTPase ARF1. Together, these data give support to a new trafficking pathway for soluble cargo that is active in adipocytes.

Downregulation of NK cell activities in Apolipoprotein C-III-induced hyperlipidemia resulting from lipid-induced metabolic reprogramming and crosstalk with lipid-laden dendritic cells

OBJECTIVE

Apolipoprotein C-III (Apoc3) is a key component of triglyceride-rich lipoproteins (TRL). The Apoc3-transgenic mice are characterized by high levels of plasma triglyceride and free fatty acids (FFAs). Apoc3 stimulates human monocytes via activation of the NLRP3 inflammasome. Considering the NK cell downregulation in obese individuals and the possible stimulatory-effects of macrophages, variations of NK cell functions and underlying mechanisms were investigated in mice with Apoc3-induced hyperlipidemia.

METHODS

Variations of activities and glycolipid metabolism in NK cells of the Apoc3-transgenic mice with hyperlipidemia were detected. Molecular mechanisms of lipid-induced metabolic-reprogramming in NK cells were analyzed based on the transcriptome sequencing. Finally, effects of DCs in mice with hyperlipidemia on NK cell functions were determined.

RESULTS

Impaired number and function of NK cells in Apoc3^TG mice was involved with the increased fatty acid oxidation and decreased glycolysis. Increased uptake of FFAs in Apoc3^TG-NK cells contributed to the peroxisome proliferator-activated receptor (PPAR) activation and the downstream PTEN-AKT-mTOR/FOXO1 signaling pathway. Inhibition of PPAR or CPT1α only partly reversed the IFN-γ production of Apoc3^TG-NK cells, but completely restored IFN-γ secretion by palmitic acid-treated NK cells ex vivo, indicating that other factors contributed to the Apoc3^TG-NK cell downregulation. Meanwhile, Apoc3^TG-DCs, which contained more lipids in the cytoplasm, depended on reactive oxygen species (ROS) to increase the expressions PD-L1, TGF-β1, and NKG2D ligands and suppress NK cell activities. DCs of the Apoc3^TG-CD36^-/+ hybrid mice with less intracellular lipids and ROS production could not inhibit NK cells, indicating that intracellular FFAs promoted the immune-modulatory function of DCs.

CONCLUSIONS

The downregulation of NK cell activities in individuals with Apoc3-induced hyperlipidemia was due to the increased fatty acid oxidation in NK cells and the bystander suppression caused by lipid-laden DCs. The dual recovery function of NK cells and DCs would improve the prognosis of patients with metabolic syndrome.

Lipoprotein Lipase Overexpression in Skeletal Muscle Attenuates Weight Regain by Potentiating Energy Expenditure

Moderate weight loss improves numerous risk factors for cardiometabolic disease; however, long-term weight loss maintenance (WLM) is often thwarted by metabolic adaptations that suppress energy expenditure and facilitate weight regain. Skeletal muscle has a prominent role in energy homeostasis; therefore, we investigated the effect of WLM and weight regain on skeletal muscle in rodents. In skeletal muscle of obesity-prone rats, WLM reduced fat oxidative capacity and downregulated genes involved in fat metabolism. Interestingly, even after weight was regained, genes involved in fat metabolism were also reduced. We then subjected mice with skeletal muscle lipoprotein lipase overexpression (mCK-hLPL), which augments fat metabolism, to WLM and weight regain and found that mCK-hLPL attenuates weight regain by potentiating energy expenditure. Irrespective of genotype, weight regain suppressed dietary fat oxidation and downregulated genes involved in fat metabolism in skeletal muscle. However, mCK-hLPL mice oxidized more fat throughout weight regain and had greater expression of genes involved in fat metabolism and lower expression of genes involved in carbohydrate metabolism during WLM and regain. In summary, these results suggest that skeletal muscle fat oxidation is reduced during WLM and regain, and therapies that improve skeletal muscle fat metabolism may attenuate rapid weight regain.

The effects of prepartum energy intake and peripartum rumen-protected choline supplementation on hepatic genes involved in glucose and lipid metabolism

Nutritional interventions, either by controlling dietary energy (DE) or supplementing rumen-protected choline (RPC) or both, may mitigate negative postpartum metabolic health outcomes. A companion paper previously reported the effects of DE density and RPC supplementation on production and health outcomes. The objective of this study was to examine the effects of DE and RPC supplementation on the expression of hepatic oxidative, gluconeogenic, and lipid transport genes during the periparturient period. At 47 ± 6 d relative to calving (DRTC), 93 multiparous Holstein cows were randomly assigned in groups to dietary treatments in a 2 × 2 factorial of (1) excess energy (EXE) without RPC supplementation (1.63 Mcal of NE_L/kg of dry matter; EXE-RPC); (2) maintenance energy (MNE) without RPC supplementation (1.40 Mcal of NE_L/kg dry matter; MNE-RPC); (3) EXE with RPC supplementation (EXE+RPC); and (4) MNE with RPC supplementation (MNE+RPC). To achieve the objective of this research, liver biopsy samples were collected at -14, +7, +14, and +21 DRTC and analyzed for mRNA expression (n = 16/treatment). The interaction of DE × RPC decreased glucose-6-phosphatase and increased peroxisome proliferator-activated receptor α in MNE+RPC cows. Expression of cytosolic phosphoenolpyruvate carboxykinase was altered by the interaction of dietary treatments with reduced expression in EXE+RPC cows. A dietary treatment interaction was detected for expression of pyruvate carboxylase although means were not separated. Dietary treatment interactions did not alter expression of carnitine palmitoyltransferase 1A or microsomal triglyceride transfer protein. The 3-way interaction of DE × RPC × DRTC affected expression of carnitine palmitoyltransferase 1A, glucose-6-phosphatase, and peroxisome proliferator-activated receptor α and tended to affect cytosolic phosphoenolpyruvate carboxykinase. Despite previously reported independent effects of DE and RPC on production variables, treatments interacted to influence hepatic metabolism through altered gene expression.

The interplay between non-esterified fatty acids and bovine peroxisome proliferator-activated receptors: results of an in vitro hybrid approach

Background

In dairy cows circulating non-esterified fatty acids (NEFA) increase early post-partum while liver and other tissues undergo adaptation to greater lipid metabolism, mainly regulated by peroxisome proliferator-activated receptors (PPAR). PPAR are activated by fatty acids (FA), but it remains to be demonstrated that circulating NEFA or dietary FA activate bovine PPAR. We hypothesized that circulating NEFA and dietary FA activate PPAR in dairy cows.

Methods

The dose-response activation of PPAR by NEFA or dietary FA was assessed using HP300e digital dispenser and luciferase reporter in several bovine cell types. Cells were treated with blood plasma isolated from Jersey cows before and after parturition, NEFA isolated from the blood plasma, FA released from lipoproteins using milk lipoprotein lipase (LPL), and palmitic acid (C16:0). Effect on each PPAR isotype was assessed using specific synthetic inhibitors.

Results

NEFA isolated from blood serum activate PPAR linearly up to ~ 4-fold at 400 μmol/L in MAC-T cells but had cytotoxic effect. Addition of albumin to the culture media decreases cytotoxic effects of NEFA but also PPAR activation by ~ 2-fold. Treating cells with serum from peripartum cows reveals that much of the PPAR activation can be explained by the amount of NEFA in the serum (R² = 0.91) and that the response to serum NEFA follows a quadratic tendency, with peak activation around 1.4 mmol/L. Analysis of PPAR activation by serum in MAC-T, BFH-12 and BPAEC cells revealed that most of the activation is explained by the activity of PPARδ and PPARγ, but not PPARα. Palmitic acid activated PPAR when added in culture media or blood serum but the activation was limited to PPARδ and PPARα and the response was nil in serum from post-partum cows. The addition of LPL to the serum increased > 1.5-fold PPAR activation.

Conclusion

Our results support dose-dependent activation of PPAR by circulating NEFA in bovine, specifically δ and γ isotypes. Data also support the possibility of increasing PPAR activation by dietary FA; however, this nutrigenomics approach maybe only effective in pre-partum but not post-partum cows.

An Inhibitor of Fatty Acid Synthase Thioesterase Domain with Improved Cytotoxicity against Breast Cancer Cells and Stability in Plasma

It is well recognized that many cancers are addicted to a constant supply of fatty acids (FAs) and exhibit brisk de novo FA synthesis. Upregulation of a key lipogenic enzyme, fatty acid synthase (FASN), is a near-universal feature of human cancers and their precursor lesions, and has been associated with chemoresistance, tumor metastasis, and diminished patient survival. FASN inhibition has been shown to be effective in killing cancer cells, but progress in the field has been hindered by off-target effects and poor pharmaceutical properties of candidate compounds. Our initial hit (compound 1) was identified from a high-throughput screening effort by the Sanford-Burnham Center for Chemical Genomics using purified FASN thioesterase (FASN-TE) domain. Despite being a potent inhibitor of purified FASN-TE, compound 1 proved highly unstable in mouse plasma and only weakly cytotoxic to breast cancer (BC) cells in vitro. An iterative process of synthesis, cytotoxicity testing, and plasma stability assessment was used to identify a new lead (compound 41). This lead is more cytotoxic against multiple BC cell lines than tetrahydro-4-methylene-2S-octyl-5-oxo-3R-furancarboxylic acid (the literature standard for inhibiting FASN), is stable in mouse plasma, and shows negligible cytotoxic effects against nontumorigenic mammary epithelial cells. Compound 41 also has drug-like physical properties based on Lipinski's rules and is, therefore, a valuable new lead for targeting fatty acid synthesis to exploit the requirement of tumor cells for fatty acids. SIGNIFICANCE STATEMENT: An iterative process of synthesis and biological testing was used to identify a novel thioesterase domain FASN inhibitor that has drug-like properties, is more cytotoxic to breast cancer cells than the widely used tetrahydro-4-methylene-2S-octyl-5-oxo-3R-furancarboxylic acid, and has negligible effects on the growth and proliferation of noncancerous mammary epithelial cells. Our studies have confirmed the value of using potent and selective FASN inhibitors in the treatment of BC cells and have shown that the availability of exogenous lipoproteins may impact both cancer cell FA metabolism and survival.

Role of bone marrow adipocytes in leukemia and chemotherapy challenges

Adipose tissue (AT) is an extramedullary reservoir of normal hematopoietic stem cells (HSCs). Adipocytes prevent the production of normal HSCs via secretion of inflammatory factors, and adipocyte-derived free fatty acids may contribute to the development and progression of leukemia via providing energy for leukemic cells. In addition, adipocytes are able to metabolize and inactivate therapeutic agents, reducing the concentrations of active drugs in adipocyte-rich microenvironments. The aim of this study was to detect the role of adipocytes in the progression and treatment of leukemia. Relevant literature was identified through a PubMed search (2000-2018) of English-language papers using the following terms: leukemia, adipocyte, leukemic stem cell, chemotherapy, and bone marrow. Findings suggest the striking interplay between leukemic cells and adipocytes to create a unique microenvironment supporting the metabolic demands and survival of leukemic cells. Based on these findings, targeting lipid metabolism of leukemic cells and adipocytes in combination with standard therapeutic agents might present novel treatment options.

Anti-Hypertensive Action of Fenofibrate via UCP2 Upregulation Mediated by PPAR Activation in Baroreflex Afferent Pathway

Fenofibrate, an agonist for peroxisome proliferator-activated receptor alpha (PPAR-α), lowers blood pressure, but whether this action is mediated via baroreflex afferents has not been elucidated. In this study, the distribution of PPAR-α and PPAR-γ was assessed in the nodose ganglion (NG) and the nucleus of the solitary tract (NTS). Hypertension induced by drinking high fructose (HFD) was reduced, along with complete restoration of impaired baroreceptor sensitivity, by chronic treatment with fenofibrate. The molecular data also showed that both PPAR-α and PPAR-γ were dramatically up-regulated in the NG and NTS of the HFD group. Expression of the downstream signaling molecule of PPAR-α, the mitochondrial uncoupling protein 2 (UCP2), was up-regulated in the baroreflex afferent pathway under similar experimental conditions, along with amelioration of reduced superoxide dismutase activity and increased superoxide in HFD rats. These results suggest that chronic treatment with fenofibrate plays a crucial role in the neural control of blood pressure by improving baroreflex afferent function due at least partially to PPAR-mediated up-regulation of UCP2 expression and reduction of oxidative stress.

Altered expression of metabolic pathways in CLL detected by unlabelled quantitative mass spectrometry analysis

Chronic lymphocytic leukaemia (CLL) remains the most common incurable malignancy of B cells in the western world. Patient outcomes are heterogeneous and can be difficult to predict with current prognostic markers. Here, we used a quantitative label-free proteomic technique to ascertain differences in the B-cell proteome from healthy donors and CLL patients with either mutated (M-CLL) or unmutated (UM-CLL) IGHV to identify new prognostic markers. In peripheral B-CLL cells, 349 (22%) proteins were differentially expressed between normal B cells and B-CLL cells and 189 (12%) were differentially expressed between M-CLL and UM-CLL. We also examined the proteome of proliferating CLL cells in the lymph nodes, and identified 76 (~8%) differentially expressed proteins between healthy and CLL lymph nodes. B-CLL cells show over-expression of proteins involved in lipid and cholesterol metabolism. A comprehensive lipidomic analysis highlighted large differences in glycolipids and sphingolipids. A shift was observed from the pro-apoptotic lipid ceramide towards the anti-apoptotic/chemoresistant lipid, glucosylceramide, which was more evident in patients with aggressive disease (UM-CLL). This study details a novel quantitative proteomic technique applied for the first time to primary patient samples in CLL and highlights that primary CLL lymphocytes display markers of a metabolic shift towards lipid synthesis and breakdown.

Symposium review: Milk fat globule size: Practical implications and metabolic regulation

Milk fat globule (MFG) size ranges over 3 orders of magnitude, from less than 200 nm to over 15 µm. The significance of MFG size derives from its tight association with its lipidome and proteome. More specifically, small MFG have relatively higher content of membrane compared with large globules, and this membrane exerts diverse positive health effects, as reported in human and animal studies. In addition, MFG size has industrial significance, as it affects the physicochemical and sensory characteristics of dairy products. Studies on the size regulation of MFG are scarce, mainly because various confounders indirectly affect MFG size. Because MFG size is determined before and during its secretion from mammary epithelial cells, studies on the size regulation of its precursors, the intracellular lipid droplets (LD), have been used as a proxy for understanding the mechanisms controlling MFG size. In this review, we provide evidence for 2 distinct mechanisms regulating LD size in mammary epithelial cells: co-regulation of fat content and triglyceride-synthesis capacity of the cells, and fusion between LD. The latter is controlled by the membrane's polar lipid composition and involves mitochondrial enzymes. Accordingly, this review also discusses MFG size regulation in the in vivo metabolic context, as MFG morphometric features are often modulated under conditions that involve animals' altered energy status.

Changes in lipid droplets morphometric features in mammary epithelial cells upon exposure to non-esterified free fatty acids compared with VLDL

The effects of the macrostructure of long chain fatty acids on the lipid metabolism and biosynthesis of lipid droplets (LD) was studied in mammary epithelial cells (MEC). MEC were exposed to similar compositions and concentrations of fatty acids in the form of either triglycerides (Tg), as part of the very-low-density lipids (VLDL) isolated from lactating cow plasma, or as non-esterified- free fatty acids (FFA). Exposing MEC to FFA resulted in two distinct processes; each independently could increase LD size: an elevation in Tg production and alterations in phospholipid (PL) composition. In particular, the lower PC/PE ratio in the FFA treatment indicated membrane destabilization, which was concomitant with the biosynthesis of larger LD. In addition, 6 fold increase in the cellular concentration of the exogenously added linoleic acid (C18:2) was found in MEC treated with FFA, implying that long chain fatty acids administrated as FFA have higher availability to MEC, enabling greater PL synthesis, more material for the LD envelope, thereby enhancing LD formation. Availability of long chain fatty acids administrated as VLDL-Tg, is dependent on LPL which its activity can be inhibited by the hydrolysis products. Therefore, we used increasing concentrations of albumin, to reduce the allosteric inhibition on LPL by the hydrolysis products. Indeed, a combined treatment of VLDL and albumin, increased LD size and number, similar to the phenotype found in the FFA treatment. These results reveal the role played by the macrostructure of long chain fatty acids in the regulation of LD size in MEC which determine the size of the secreted MFG.

Extrahepatic PPARα modulates fatty acid oxidation and attenuates fasting-induced hepatosteatosis in mice

PPARα (PPARA), expressed in most oxidative tissues, is a major regulator of lipid homeostasis; hepatic PPARA plays a critical role during the adaptive fasting response by promoting FA oxidation (FAO). To clarify whether extrahepatic PPARA activity can protect against lipid overload when hepatic PPARA is impaired, lipid accumulation was compared in WT (Ppara ^+/+), total body Ppara-null (Ppara ^-/-), and hepatocyte-specific Ppara-null (Ppara ^ΔHep) mice that were fasted for 24 h. Histologic staining indicated reduced lipid accumulation in Ppara ^ΔHep versus Ppara ^-/- mice, and biochemical analyses revealed diminished medium- and long-chain FA accumulation in Ppara ^ΔHep mouse livers. Hepatic PPARA target genes were suppressed in both mouse models. Serum FFAs increased in all genotypes after fasting but were highest in Ppara ^-/- mice. In Ppara ^ΔHep mice, FAO genes were increased in brown adipose tissue, heart, and muscle, and total lipase activity was elevated in the muscle and heart, suggesting increased lipid utilization. Thus, extrahepatic PPARA activity reduces systemic lipid load when hepatic lipid metabolism is impaired by elevating FAO and lipase activity in other tissues and, as a result, protects against fasting-induced hepatosteatosis. This has important clinical implications in disease states with impaired hepatic PPARA function, such as nonalcoholic steatohepatitis and nonalcoholic fatty liver disease.

Abnormal lipoprotein oxylipins in metabolic syndrome and partial correction by omega-3 fatty acids

Metabolic syndrome (MetSyn) is characterized by chronic inflammation which mediates the associated high risk for cardiovascular and other diseases. Oxylipins are a superclass of lipid mediators with potent bioactivities in inflammation, vascular biology, and more. While their role as locally produced agents is appreciated, most oxylipins in plasma are found in lipoproteins suggesting defective regulation of inflammation could be mediated by the elevated VLDL and low HDL levels characteristic of MetSyn. Our objective was to compare the oxylipin composition of VLDL, LDL, and HDL in 14 optimally healthy individuals and 31 MetSyn patients, and then to determine the effects of treating MetSyn subjects with 4g/day of prescription omega-3 fatty acids (P-OM3) on lipoprotein oxylipin profiles. We compared oxylipin compositions of healthy (14) and MetSyn (31) subjects followed by randomization and assignment to 4g/d P-OM3 for 16 weeks using LC/MS/MS. Compared to healthy subjects, MetSyn is characterized by abnormalities of (1) pro-inflammatory, arachidonate-derived oxylipins from the lipoxygenase pathway in HDL; and (2) oxylipins mostly not derived from arachidonate in VLDL. P-OM3 treatment corrected many components of these abnormalities, reducing the burden of inflammatory mediators within peripherally circulating lipoproteins that could interfere with, or enhance, local effectors of inflammatory stress. We conclude that MetSyn is associated with a disruption of lipoprotein oxylipin patterns consistent with greater inflammatory stress, and the partial correction of these dysoxylipinemias by treatment with omega-3 fatty acids could explain some of their beneficial effects.

PPAR-γ Agonists and Their Role in Primary Cicatricial Alopecia

Peroxisome proliferator-activated receptor γ (PPAR-γ) is a ligand-activated nuclear receptor that regulates the transcription of various genes. PPAR-γ plays roles in lipid homeostasis, sebocyte maturation, and peroxisome biogenesis and has shown anti-inflammatory effects. PPAR-γ is highly expressed in human sebaceous glands. Disruption of PPAR-γ is believed to be one of the mechanisms of primary cicatricial alopecia (PCA) pathogenesis, causing pilosebaceous dysfunction leading to follicular inflammation. In this review article, we discuss the pathogenesis of PCA with a focus on PPAR-γ involvement in pathogenesis of lichen planopilaris (LPP), the most common lymphocytic form of PCA. We also discuss clinical trials utilizing PPAR-agonists in PCA treatment.

Prevention Mechanism of 2,3,5,4'-Tetrahydroxy-stilbene-2-O-β-D-glucoside on Lipid Accumulation in Steatosis Hepatic L-02 Cell

AIM

2,3,5,4'-Tetrahydroxy-stilbene-2-O-β-d-glucoside (TSG), a natural stilbene, shows great activities in hepatic lipid regulation, especially for hepatic triglyceride lowering. However, information about its mechanisms on biosynthesis and degradation of triglyceride is still limited. This research pays close attention to clarify the mechanism of TSG on prevention of hepatic lipid accumulation.

MATERIALS AND METHODS

TSG was given to steatosis hepatocyte L-02 cell induced by fat emulsion incubation. The contents of free fatty acid, triglyceride, rate-controlling enzymes, and transcriptional regulatory factors, which play key role in biosynthesis and decomposition of triglyceride, were determined with or without TSG exposure.

RESULTS

TSG could reduce the free fatty acid material supply for the synthesis of endogenous triglyceride and it did so by reducing the expression of liver type fatty acid binding protein and fatty acid transport protein 4. TS Ginhibited the expression of sterol regulatory element-binding protein 1c, and then reduce the contents of acetyl-CoA carboxylase 1 and fatty acid synthase. Therefore, TSG prevented biosynthesis of triglyceride. Mean while, TSG also promoted the decomposition of triglyceride by the activation of peroxisome proliferators activator receptors alpha.

CONCLUSION

TSG could effective intervene the accumulation of triglyceride in hepatic cell. Thus, TSG could be considered as a promising drug candidate in prevention and treatment of lipid metabolic disorders, especially nonalcoholic fatty liver disease. Abbreviations Used: ACACA: Acetyl-CoA carboxylase 1, Apo-B100: Apo lipoprotein B100, FASN: Fatty acid synthase, FATP4: Fatty acid transport protein 4, FBS: Fetal bovine serum; FEN: Fenofibrate, FFA: Free fatty acid, L-FABP: Liver type fatty acid binding protein, LPL: Lipoprotein lipase, MTTP: Microsomal triglyceride transfer protein, NAFLD: Non-alcoholic fatty liver disease, PBS: Phosphate buffer saline, PPAR-α: Peroxisome proliferators activator receptors alpha, RPMI: Roswell Park Memorial Institute, SIM: Simvastatin, SREBF1c: Sterol regulatory element-binding protein 1c, TG: Triglyceride, TSG: 2, 3, 5, 4-tetrahydroxy-stilbene-2-O-β-Dglucoside, VLDL: Very low density lipoprotein.

Lipoprotein lipase liberates free fatty acids to inhibit HCV infection and prevent hepatic lipid accumulation

Lipoprotein lipase (LPL) has been identified as an anti-hepatitis C virus (HCV) host factor, but the cellular mechanism remains elusive. Here, we investigated the cellular mechanism of LPL involving in anti-HCV. The functional activation of peroxisome proliferator-activated receptor (PPAR) α signal by LPL transducing into hepatocytes was investigated in HCV-infected cells, primary human hepatocytes, and in HCV-core transgenic mice. The result showed that the levels of transcriptional transactivity and nuclear translocation of PPARα in Huh7 cells and primary human hepatocytes were elevated by physiologically ranged LPL treatment of either very-low density lipoprotein or HCV particles. The LPL-induced hepatic PPARα activation was weakened by blocking the LPL enzymatic activity, and by preventing the cellular uptake of free unsaturated fatty acids with either albumin chelator or silencing of CD36 translocase. The knockdowns of PPARα and CD36 reversed the LPL-mediated suppression of HCV infection. Furthermore, treatment with LPL, like the direct activation of PPARα, not only reduced the levels of apolipoproteins B, E, and J, which are involved in assembly and release of HCV virions, but also alleviated hepatic lipid accumulation induced by core protein. HCV-core transgenic mice exhibited more hepatic miR-27b, which negatively regulates PPARα expression, than did the wild-type controls. The induction of LPL activity by fasting in the core transgenic mice activated PPARα downstream target genes that are involved in fatty acid β-oxidation. Taken together, our study reveals dual beneficial outcomes of LPL in anti-HCV and anti-steatosis and shed light on the control of chronic hepatitis C in relation to LPL modulators.

Comprehensive insights into microcystin-LR effects on hepatic lipid metabolism using cross-omics technologies

Microcystin-LR (MC-LR) can induce hepatic tissue damages and molecular toxicities, but its effects on lipid metabolism remain unknown. This study investigated the effects of MC-LR exposure on mice lipid metabolism and uncovered the underlying mechanism through metabonomic, transcriptomic and metagenomic analyses after administration of mice with MC-LR by gavage for 28 d. Increased liver weight and abdominal fat weight, and evident hepatic lipid vacuoles accumulation were observed in the mice fed with 0.2mg/kg/d MC-LR. Serum nuclear magnetic resonance analysis showed that MC-LR treatment altered the levels of serum metabolites including triglyceride, unsaturated fatty acid (UFA) and very low density lipoprotein. Digital Gene Expression technology was used to reveal differential expression of hepatic transcriptomes, demonstrating that MC-LR treatment disturbed hepatic UFA biosynthesis and activated peroxisome proliferator-activated receptor (PPAR) signaling pathways via Pparγ, Fabp1 and Fabp2 over-expression. Metagenomic analyses of gut microbiota revealed that MC-LR exposure also increased abundant ratio of Firmicutes vs. Bacteroidetes in gut and altered biosynthetic pathways of various microbial metabolic and pro-inflammatory molecules. In conclusion, oral MC-LR exposure can induce hepatic lipid metabolism disorder mediated by UFA biosynthesis and PPAR activation, and gut microbial community shift may play an important role in the metabolic disturbance.

Cyp1b1 affects external control of mouse hepatocytes, fatty acid homeostasis and signaling involving HNF4α and PPARα

Cytochrome P450 1b1 (Cyp1b1) is expressed in endothelia, stellate cells and pre-adipocytes, but not hepatocytes. Deletion alters liver fatty acid metabolism and prevents obesity and hepatic steatosis. This suggests a novel extra-hepatocyte regulation directed from cells that express Cyp1b1. To characterize these mechanisms, microarray gene expression was analyzed in livers of normal and congenic Cyp1b1-ko C57BL/6 J mice fed either low or high fat diets. Cyp1b1-ko gene responses indicate suppression of endogenous PPARα activity, a switch from triglyceride storage to mitochondrial fatty acid oxidation and decreased oxidative stress. Many gene responses in Cyp1b1-ko are sexually dimorphic and correspond to increased activity of growth hormone mediated by HNF4α. Male responses stimulated by GH pulses are enhanced, whereas responses that decline exhibit further suppression, including Cyp regulation by PPARα, CAR and PXR. These effects of Cyp1b1 deletion overlap with effects caused by deletion of the small heterodimeric partner, a suppressor of these nuclear factors. Redirection of gene expression associated with liver fat homeostasis in Cyp1b1-ko mice that directs hypothalamic control of GH and leptin. Cyp1b1-ko suppresses neonatal Scd1 and delays adult maturation of dimorphic GH/HNF4α signaling. Alternatively, deletion may diminish hypothalamic metabolism of estradiol, which establishes adult GH regulation.

Metabolism pathways in chronic lymphocytic leukemia

Alterations in chronic lymphocytic leukemia (CLL) cell metabolism have been studied by several investigators. Unlike normal B lymphocytes or other leukemia cells, CLL cells, like adipocytes, store lipids and utilize free fatty acids (FFA) to produce chemical energy. None of the recently identified mutations in CLL directly affects metabolic pathways, suggesting that genetic alterations do not directly contribute to CLL cells' metabolic reprogramming. Conversely, recent data suggest that activation of STAT3 or downregulation of microRNA-125 levels plays a crucial role in the utilization of FFA to meet the CLL cells' metabolic needs. STAT3, known to be constitutively activated in CLL, increases the levels of lipoprotein lipase (LPL) that mediates lipoprotein uptake and shifts the CLL cells' metabolism towards utilization of FFA. Herein, we review the evidence for altered lipid metabolism, increased mitochondrial activity and formation of reactive oxygen species (ROS) in CLL cells, and discuss the possible therapeutic strategies to inhibit lipid metabolism pathways in patient with CLL.

Early Life Exposure to Fructose Alters Maternal, Fetal and Neonatal Hepatic Gene Expression and Leads to Sex-Dependent Changes in Lipid Metabolism in Rat Offspring

Aim

Fructose consumption is associated with altered hepatic function and metabolic compromise and not surprisingly has become a focus for perinatal studies. We have previously shown that maternal fructose intake results in sex specific changes in fetal, placental and neonatal outcomes. In this follow-up study we investigated effects on maternal, fetal and neonatal hepatic fatty acid metabolism and immune modulation.

Methods

Pregnant rats were randomised to either control (CON) or high-fructose (FR) diets. Fructose was given in solution and comprised 20% of total caloric intake. Blood and liver samples were collected at embryonic day 21 (E21) and postnatal day (P)10. Maternal liver samples were also collected at E21 and P10. Liver triglyceride and glycogen content was measured with standard assays. Hepatic gene expression was measured with qPCR.

Results

Maternal fructose intake during pregnancy resulted in maternal hepatic ER stress, hepatocellular injury and increased levels of genes that favour lipogenesis. These changes were associated with a reduction in the NLRP3 inflammasome. Fetuses of mothers fed a high fructose diet displayed increased hepatic fructose transporter and reduced fructokinase mRNA levels and by 10 days of postnatal age, also have hepatic ER stress, and elevated IL1β mRNA levels. At P10, FR neonates demonstrated increased hepatic triglyceride content and particularly in males, associated changes in the expression of genes regulating beta oxidation and the NLRP3 inflammasome. Further, prenatal fructose results in sex-dependant changes in levels of key clock genes.

Conclusions

Maternal fructose intake results in age and sex-specific alterations in maternal fetal and neonatal free fatty acid metabolism, which may be associated in disruptions in core clock gene machinery. How these changes are associated with hepatic inflammatory processes is still unclear, although suppression of the hepatic inflammasome, as least in mothers and male neonates may point to impaired immune sensing.

Aberrant LPL Expression, Driven by STAT3, Mediates Free Fatty Acid Metabolism in CLL Cells

While reviewing chronic lymphocytic leukemia (CLL) bone marrow slides, we identified cytoplasmic lipid vacuoles in CLL cells but not in normal B cells. Because lipoprotein lipase (LPL), which catalyzes hydrolysis of triglycerides into free fatty acids (FFA), is aberrantly expressed in CLL, we investigated whether LPL regulates the oxidative metabolic capacity of CLL cells. We found that unlike normal B cells, CLL cells metabolize FFAs. Because STAT3 is constitutively activated in CLL cells and because we identified putative STAT3 binding sites in the LPL promoter, we sought to determine whether STAT3 drives the aberrant expression of LPL. Transfection of luciferase reporter gene constructs driven by LPL promoter fragments into MM1 cells revealed that STAT3 activates the LPL promoter. In addition, chromatin immunoprecipitation confirmed that STAT3 binds to the LPL promoter. Furthermore, transfection of CLL cells with STAT3-shRNA downregulated LPL transcripts and protein levels, confirming that STAT3 activates the LPL gene. Finally, transfection of CLL cells with LPL-siRNAs decreased the capacity of CLL cells to oxidize FFAs and reduced cell viability.

IMPLICATIONS

Our study suggests that CLL cells adopt their metabolism to oxidize FFA. Activated STAT3 induces LPL, which catalyzes the hydrolysis of triglycerides into FFA. Therefore, inhibition of STAT3 is likely to prevent the capacity of CLL cells to utilize FFA.

Lipoprotein lipase, tissue expression and effects on genes related to fatty acid synthesis in goat mammary epithelial cells

Lipoprotein lipase (LPL) serves as a central factor in hydrolysis of triacylglycerol and uptake of free fatty acids from the plasma. However, there are limited data concerning the action of LPL on the regulation of milk fat synthesis in goat mammary gland. In this investigation, we describe the cloning and sequencing of the LPL gene from Xinong Saanen dairy goat mammary gland, along with a study of its phylogenetic relationships. Sequence analysis showed that goat LPL shares similarities with other species including sheep, bovine, human and mouse. LPL mRNA expression in various tissues determined by RT-qPCR revealed the highest expression in white adipose tissue, with lower expression in heart, lung, spleen, rumen, small intestine, mammary gland, and kidney. Expression was almost undetectable in liver and muscle. The expression profiles of LPL gene in mammary gland at early, peak, mid, late lactation, and the dry period were also measured. Compared with the dry period, LPL mRNA expression was markedly greater at early lactation. However, compared with early lactation, the expression was lower at peak lactation and mid lactation. Despite those differences, LPL mRNA expression was still greater at peak, mid, and late lactation compared with the dry period. Using goat mammary epithelial cells (GMEC), the in vitro knockdown of LPL via shRNA or with Orlistat resulted in a similar degree of down-regulation of LPL (respectively). Furthermore, knockdown of LPL was associated with reduced mRNA expression of SREBF1, FASN, LIPE and PPARG but greater expression of FFAR3. There was no effect on ACACA expression. Orlistat decreased expression of LIPE, FASN, ACACA, and PPARG, and increased FFAR3 and SREBF1 expression. The pattern of LPL expression was similar to the changes in milk fat percentage in lactating goats. Taken together, results suggest that LPL may play a crucial role in fatty acid synthesis.

Effect of omega-3 fatty acid ethyl esters on the oxylipin composition of lipoproteins in hypertriglyceridemic, statin-treated subjects

Background

Oxylipins mediate inflammation, vascular tension, and more. Their presence in lipoproteins could explain why lipoproteins mediate nearly identical activities.

Methods

To determine how oxylipins are distributed in the lipoproteins of hypertriglyceridemic subjects, and whether omega-3 fatty acids alter them in a manner consistent with improved cardiovascular health, we recruited 15 dyslipidemic subjects whose levels of low density lipoprotein cholesterol (LDL-C) were at goal but who remained hypertriglyceridemic (200–499 mg/dL). They were treated them with the indicated dose of 4 g/d omega-3 acid ethyl esters (P-OM3) for 8 weeks. Measured oxylipins included mid-chain alcohols (HETEs, HEPEs and HDoHEs), ketones (KETEs), epoxides (as EpETrEs, EpETEs, and EpDPEs).

Results

At baseline, arachidonate-oxylipins (HETEs, KETEs, and EpETrEs) were most abundant in plasma with the greatest fraction of total abundance (mean |95% CI|) being carried in high density lipoproteins (HDL); 42% |31, 57| followed by very low density lipoproteins (VLDL); 27% |20, 36|; and LDL 21% |16, 28|. EPA- and DHA-derived oxylipins constituted less than 11% of total. HDL carried alcohols and epoxides but VLDL was also rich in ketones. Treatment decreased AA-derived oxylipins across lipoprotein classes (−23% |−33, −12|, p = 0.0003), and expanded EPA−(322% |241, 422|, p<0.0001) and DHA-derived oxylipins (123% |80, 176|, p<0.0001).

Conclusions

Each lipoprotein class carries a unique oxylipin complement. P-OM3 treatment alters the oxylipin content of all classes, reducing pro-inflammatory and increasing anti-inflammatory species, consistent with the improved inflammatory and vascular status associated with the treatment.

Trial Registration

ClinicalTrials.gov NCT00959842

Lipoprotein lipase: from gene to atherosclerosis

Lipoprotein lipase (LPL) is a key enzyme in lipid metabolism and responsible for catalyzing lipolysis of triglycerides in lipoproteins. LPL is produced mainly in adipose tissue, skeletal and heart muscle, as well as in macrophage and other tissues. After synthesized, it is secreted and translocated to the vascular lumen. LPL expression and activity are regulated by a variety of factors, such as transcription factors, interactive proteins and nutritional state through complicated mechanisms. LPL with different distributions may exert distinct functions and have diverse roles in human health and disease with close association with atherosclerosis. It may pose a pro-atherogenic or an anti-atherogenic effect depending on its locations. In this review, we will discuss its gene, protein, synthesis, transportation and biological functions, and then focus on its regulation and relationship with atherosclerosis and potential underlying mechanisms. The goal of this review is to provide basic information and novel insight for further studies and therapeutic targets.

Lipids and the endothelium: bidirectional interactions

The endothelium is often viewed solely as the barrier that prevents the penetration of circulating lipoproteins into the arterial wall. However, recent research has demonstrated that the endothelium has an important part in regulating circulating fatty acids and lipoproteins, and is in turn affected by these lipids/lipoproteins in ways that appear to have important repercussions for atherosclerosis. Thus, a number of potentially toxic lipids are produced during lipolysis of lipoproteins at the endothelial cell surface. Catabolism of triglyceride-rich lipoproteins creates free fatty acids that are readily taken up by endothelial cells, and, likely through the action of acyl-CoA synthetases, exacerbate inflammatory processes. In this article, we review how the endothelium participates in lipoprotein metabolism, how lipids alter endothelial functions, and how lipids are internalized, processed, and transported into the subendothelial space. Finally, we address the many endothelial changes that might promote atherogenesis, especially in the setting of diabetes.

Transcriptomic profiling as a screening tool to detect trenbolone treatment in beef cattle

The effects of steroid hormone implants containing trenbolone alone (Finaplix-H), combined with 17β-oestradiol (17β-E; Revalor-H), or with 17β-E and dexamethasone (Revalor-H plus dexamethasone per os) on the bovine muscle transcriptome were examined by DNA-microarray. Overall, large sets of genes were shown to be modulated by the different growth promoters (GPs) and the regulated pathways and biological processes were mostly shared among the treatment groups. Using the Prediction Analysis of Microarray program, GP-treated animals were accurately identified by a small number of predictive genes. A meta-analysis approach was also carried out for the Revalor group to potentially increase the robustness of class prediction analysis. After data pre-processing, a high level of accuracy (90%) was obtained in the classification of samples, using 105 predictive gene markers. Transcriptomics could thus help in the identification of indirect biomarkers for anabolic treatment in beef cattle to be applied for the screening of muscle samples collected after slaughtering.

Very low-density lipoprotein/lipo-viro particles reverse lipoprotein lipase-mediated inhibition of hepatitis C virus infection via apolipoprotein C-III

OBJECTIVE

Circulating hepatitis C virus (HCV) virions are associated with triglyceride-rich lipoproteins, including very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL), designated as lipo-viro-particles (LVPs). Previous studies showed that lipoprotein lipase (LPL), a key enzyme for hydrolysing the triglyceride in VLDL to finally become LDL, may suppress HCV infection. This investigation considers the regulation of LPL by lipoproteins and LVPs, and their roles in the LPL-mediated anti-HCV function.

DESIGN

The lipoproteins were fractionated from normolipidemic blood samples using iodixanol gradients. Subsequent immunoglobulin-affinity purification from the canonical VLDL and LDL yielded the corresponding VLDL-LVP and LDL-LVP. Apolipoprotein (apo) Cs, LPL activity and HCV infection were quantified.

RESULTS

A higher triglyceride/cholesterol ratio of LDL was found more in HCV-infected donors than in healthy volunteers, and the triglyceride/cholesterol ratio of LDL-LVP was much increased, suggesting that the LPL hydrolysis of triglyceride may be impaired. VLDL, VLDL-LVP, LDL-LVP, but not LDL, suppressed LPL lipolytic activity, which was restored by antibodies that recognised apoC-III/-IV and correlated with the steadily abundant apoC-III/-IV quantities in those particles. In a cell-based system, treatment with VLDL and LVPs reversed the LPL-mediated inhibition of HCV infection in apoC-III/-IV-dependent manners. A multivariate logistic regression revealed that plasma HCV viral loads correlated negatively with LPL lipolytic activity, but positively with the apoC-III content of VLDL. Additionally, apoC-III in VLDL was associated with a higher proportion of HCV-RNA than was IgG.

CONCLUSION

This study reveals that LPL is an anti-HCV factor, and that apoC-III in VLDL and LVPs reduces the LPL-mediated inhibition of HCV infection.

The Effect of Unsaturated Fatty Acids on Molecular Markers of Cholesterol Homeostasis in THP-1 Macrophages

Background

Macrophages derived foam cells are key factors in the maladaptive immune and inflammatory response.

Objectives

The study of the cholesterol homeostasis and the molecular factor involved in these cells is very important in understanding the process of atherosclerosis and the mechanisms that prevent its occurrence.

Materials and Methods

This experimental study investigated the effects of c9, t11-Conjugated Linoleic Acid (c9, t11-CLA). Alpha Linolenic Acid (LA), and Eicosapentaenoic Acid (EPA) on the PPARα and ACAT1 mRNA expression by Real time PCR and cholesterol homeostasis in THP-1 macrophages derived foam cells.

Results

Incubation of CLA, LA, EPA, and synthetic ligands did not prevent increasing the cellular total cholesterol (TC). Free cholesterol (FC) is increased by Sandoz58-035 (P = 0.024) and decreased by fatty acids and Wy14643 (Pirinixic acid) (P = 0.035). The pattern of distribution of %EC is similar to the EC pattern distribution. The ACAT1 mRNA expression was significantly increased by EPA (P = 0.009), but c9, t11- CLA, LA, Wy14643, and Sandoz58-035 had no significant effect on the mRNA level of ACAT1 expression compared to DMSO(Dimethyl sulfoxide).

Discussions

In comparison to the control of Wy14643, Sandoz58-035, c9 and t11-CLA, EPA increased the PPARα mRNA levels (P = 0.024, P = 0.041, P = 0.043, and P = 0.004, respectively), even though, LA had no significant effect on the PPARα mRNA expression (P = 0.489).

Conclusions

Variations in the chemical structure of fatty acids can affect their physiological function.

Functional Role of PPARs in Ruminants: Potential Targets for Fine-Tuning Metabolism during Growth and Lactation

Characterization and biological roles of the peroxisome proliferator-activated receptor (PPAR) isotypes are well known in monogastrics, but not in ruminants. However, a wealth of information has accumulated in little more than a decade on ruminant PPARs including isotype tissue distribution, response to synthetic and natural agonists, gene targets, and factors affecting their expression. Functional characterization demonstrated that, as in monogastrics, the PPAR isotypes control expression of genes involved in lipid metabolism, anti-inflammatory response, development, and growth. Contrary to mouse, however, the PPARγ gene network appears to controls milk fat synthesis in lactating ruminants. As in monogastrics, PPAR isotypes in ruminants are activated by long-chain fatty acids, therefore, making them ideal candidates for fine-tuning metabolism in this species via nutrients. In this regard, using information accumulated in ruminants and monogastrics, we propose a model of PPAR isotype-driven biological functions encompassing key tissues during the peripartal period in dairy cattle.

Genetic and structure-function studies of missense mutations in human endothelial lipase

Endothelial lipase (EL) plays a pivotal role in HDL metabolism. We sought to characterize EL and its interaction with HDL as well as its natural variants genetically, functionally and structurally. We screened our biethnic population sample (n = 802) for selected missense mutations (n = 5) and identified T111I as the only common variant. Multiple linear regression analyses in Hispanic subjects revealed an unexpected association between T111I and elevated LDL-C (p-value = 0.012) and total cholesterol (p-value = 0.004). We examined lipase activity of selected missense mutants (n = 10) and found different impacts on EL function, ranging from normal to complete loss of activity. EL-HDL lipidomic analyses indicated that EL has a defined remodeling of HDL without exhaustion of the substrate and a distinct and preference for several fatty acids that are lipid mediators and known for their potent pro- and anti-inflammatory properties. Structural studies using homology modeling revealed a novel α/β motif in the C-domain, unique to EL. The EL dimer was found to have the flexibility to expand and to bind various sizes of HDL particles. The likely impact of the all known missense mutations (n = 18) on the structure of EL was examined using molecular modeling and the impact they may have on EL lipase activity using a novel structure-function slope based on their structural free energy differences. The results of this multidisciplinary approach delineated the impact of EL and its variants on HDL. Moreover, the results suggested EL to have the capacity to modulate vascular health through its role in fatty acid-based signaling pathways.

Targeted deletion of fibrinogen like protein 1 reveals a novel role in energy substrate utilization

Fibrinogen like protein 1(Fgl1) is a secreted protein with mitogenic activity on primary hepatocytes. Fgl1 is expressed in the liver and its expression is enhanced following acute liver injury. In animals with acute liver failure, administration of recombinant Fgl1 results in decreased mortality supporting the notion that Fgl1 stimulates hepatocyte proliferation and/or protects hepatocytes from injury. However, because Fgl1 is secreted and detected in the plasma, it is possible that the role of Fgl1 extends far beyond its effect on hepatocytes. In this study, we show that Fgl1 is additionally expressed in brown adipose tissue. We find that signals elaborated following liver injury also enhance the expression of Fgl1 in brown adipose tissue suggesting that there is a cross talk between the injured liver and adipose tissues. To identify extra hepatic effects, we generated Fgl1 deficient mice. These mice exhibit a phenotype suggestive of a global metabolic defect: Fgl1 null mice are heavier than wild type mates, have abnormal plasma lipid profiles, fasting hyperglycemia with enhanced gluconeogenesis and exhibit differences in white and brown adipose tissue morphology when compared to wild types. Because Fgl1 shares structural similarity to Angiopoietin like factors 2, 3, 4 and 6 which regulate lipid metabolism and energy utilization, we postulate that Fgl1 is a member of an emerging group of proteins with key roles in metabolism and liver regeneration.

Conjugated linoleic acid isomers and their precursor fatty acids regulate peroxisome proliferator-activated receptor subtypes and major peroxisome proliferator responsive element-bearing target genes in HepG2 cell model

The purpose of this study was to examine the induction profiles (as judged by quantitative reverse transcription polymerase chain reaction (qRT-PCR)) of peroxisome proliferator-activated receptor (PPAR) α, β, γ subtypes and major PPAR-target genes bearing a functional peroxisome proliferator responsive element (PPRE) in HepG2 cell model upon feeding with cis-9,trans-11-octadecadienoic acid (9-CLA) or trans-10,cis-12-octadecadienoic acid (10-CLA) or their precursor fatty acids (FAs). HepG2 cells were treated with 100 μmol/L 9-CLA or 10-CLA or their precursor FAs, viz., oleic, linoleic, and trans-11-vaccenic acids against bezafibrate control to evaluate the induction/expression profiles of PPAR α, β, γ subtypes and major PPAR-target genes bearing a functional PPRE, i.e., fatty acid transporter (FAT), glucose transporter-2 (GLUT-2), liver-type FA binding protein (L-FABP), acyl CoA oxidase-1 (ACOX-1), and peroxisomal bifunctional enzyme (PBE) with reference to β-actin as house keeping gene. Of the three housekeeping genes (glyceraldehyde 3-phosphate dehydrogenase (GAPDH), β-actin, and ubiquitin), β-actin was found to be stable. Dimethyl sulfoxide (DMSO), the common solubilizer of agonists, showed a significantly higher induction of genes analyzed. qRT-PCR profiles of CLAs and their precursor FAs clearly showed upregulation of FAT, GLUT-2, and L-FABP (~0.5-2.0-fold). Compared to 10-CLA, 9-CLA decreased the induction of the FA metabolizing gene ACOX-1 less than did PBE, while 10-CLA decreased the induction of PBE less than did ACOX-1. Both CLAs and precursor FAs upregulated PPRE-bearing genes, but with comparatively less or marginal activation of PPAR subtypes. This indicates that the binding of CLAs and their precursor FAs to PPAR subtypes results in PPAR activation, thereby induction of the target transporter genes coupled with downstream lipid metabolising genes such as ACOX-1 and PBE. To sum up, the expression profiles of these candidate genes showed that CLAs and their precursor FAs are involved in lipid signalling by modulating the PPAR α, β, or γ subtype for the indirect activation of the PPAR-target genes, which may in turn be responsible for the supposed health effects of CLA, and that care should be taken while calculating the actual fold induction values of candidate genes with reference to housekeeping gene and DMSO as they may impart false positive results.

Gluten-free diet reduces adiposity, inflammation and insulin resistance associated with the induction of PPAR-alpha and PPAR-gamma expression

Gluten exclusion (protein complex present in many cereals) has been proposed as an option for the prevention of diseases other than coeliac disease. However, the effects of gluten-free diets on obesity and its mechanisms of action have not been studied. Thus, our objective was to assess whether gluten exclusion can prevent adipose tissue expansion and its consequences. C57BL/6 mice were fed a high-fat diet containing 4.5% gluten (Control) or no gluten (GF). Body weight and adiposity gains, leukocyte rolling and adhesion, macrophage infiltration and cytokine production in adipose tissue were assessed. Blood lipid profiles, glycaemia, insulin resistance and adipokines were measured. Expression of the PPAR-α and γ, lipoprotein lipase (LPL), hormone sensitive lipase (HSL), carnitine palmitoyl acyltransferase-1 (CPT-1), insulin receptor, GLUT-4 and adipokines were assessed in epidydimal fat. Gluten-free animals showed a reduction in body weight gain and adiposity, without changes in food intake or lipid excretion. These results were associated with up-regulation of PPAR-α, LPL, HSL and CPT-1, which are related to lipolysis and fatty acid oxidation. There was an improvement in glucose homeostasis and pro-inflammatory profile-related overexpression of PPAR-γ. Moreover, intravital microscopy showed a lower number of adhered cells in the adipose tissue microvasculature. The overexpression of PPAR-γ is related to the increase of adiponectin and GLUT-4. Our data support the beneficial effects of gluten-free diets in reducing adiposity gain, inflammation and insulin resistance. The data suggests that diet gluten exclusion should be tested as a new dietary approach to prevent the development of obesity and metabolic disorders.

Fatty acids bind tightly to the N-terminal domain of angiopoietin-like protein 4 and modulate its interaction with lipoprotein lipase

Angiopoietin-like protein 4 (Angptl4), a potent regulator of plasma triglyceride metabolism, binds to lipoprotein lipase (LPL) through its N-terminal coiled-coil domain (ccd-Angptl4) inducing dissociation of the dimeric enzyme to inactive monomers. In this study, we demonstrate that fatty acids reduce the inactivation of LPL by Angptl4. This was the case both with ccd-Angptl4 and full-length Angptl4, and the effect was seen in human plasma or in the presence of albumin. The effect decreased in the sequence oleic acid > palmitic acid > myristic acid > linoleic acid > linolenic acid. Surface plasmon resonance, isothermal titration calorimetry, fluorescence, and chromatography measurements revealed that fatty acids bind with high affinity to ccd-Angptl4. The interactions were characterized by fast association and slow dissociation rates, indicating formation of stable complexes. The highest affinity for ccd-Angptl4 was detected for oleic acid with a subnanomolar equilibrium dissociation constant (K(d)). The K(d) values for palmitic and myristic acid were in the nanomolar range. Linoleic and linolenic acid bound with much lower affinity. On binding of fatty acids, ccd-Angptl4 underwent conformational changes resulting in a decreased helical content, weakened structural stability, dissociation of oligomers, and altered fluorescence properties of the Trp-38 residue that is located close to the putative LPL-binding region. Based on these results, we propose that fatty acids play an important role in modulating the effects of Angptl4.

Lipolytic products activate peroxisome proliferator-activated receptor (PPAR) α and δ in brown adipocytes to match fatty acid oxidation with supply

β-Adrenergic receptors (β-ARs) promote brown adipose tissue (BAT) thermogenesis by mobilizing fatty acids and inducing the expression of oxidative genes. β-AR activation increases the expression of oxidative genes by elevating cAMP, but whether lipolytic products can modulate gene expression is not known. This study examined the role that adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) plays in the induction of gene expression. Activation of brown adipocytes by β-AR agonism or 8-bromo-cyclic AMP increased the expression of PGC1α, PDK4, PPARα, uncoupling protein 1 (UCP1), and neuron-derived orphan receptor-1 (NOR-1), and concurrent inhibition of HSL reduced the induction of PGC1α, PDK4, PPARα, and UCP1 but not NOR-1. Similar results were observed in the BAT of mice following pharmacological or genetic inhibition of HSL and in brown adipocytes with stable knockdown of ATGL. Conversely, treatments that increase endogenous fatty acids elevated the expression of oxidative genes. Pharmacological antagonism and siRNA knockdown indicate that PPARα and PPARδ modulate the induction of oxidative genes by β-AR agonism. Using a live cell fluorescent reporter assay of PPAR activation, we demonstrated that ligands for PPARα and -δ, but not PPARγ, were rapidly generated at the lipid droplet surface and could transcriptionally activate PPARα and -δ. Knockdown of ATGL reduced cAMP-mediated induction of genes involved in fatty acid oxidation and oxidative phosphorylation. Consequently, ATGL knockdown reduced maximal oxidation of fatty acids, but not pyruvate, in response to cAMP stimulation. Overall, the results indicate that lipolytic products can activate PPARα and PPARδ in brown adipocytes, thereby expanding the oxidative capacity to match enhanced fatty acid supply.

Multiple sclerosis is not a disease of the immune system

Multiple sclerosis is a complex neurodegenerative disease, thought to arise through autoimmunity against antigens of the central nervous system. The autoimmunity hypothesis fails to explain why genetic and environmental risk factors linked to the disease in one population tend to be unimportant in other populations. Despite great advances in documenting the cell and molecular mechanisms underlying MS pathophysiology, the autoimmunity framework has also been unable to develop a comprehensive explanation of the etiology of the disease. I propose a new framework for understanding MS as a dysfunction of the metabolism of lipids. Specifically, the homeostasis of lipid metabolism collapses during acute-phase inflammatory response triggered by a pathogen, trauma, or stress, starting a feedback loop of increased oxidative stress, inflammatory response, and proliferation of cytoxic foam cells that cross the blood brain barrier and both catabolize myelin and prevent remyelination. Understanding MS as a chronic metabolic disorder illuminates four aspects of disease onset and progression: 1) its pathophysiology; 2) genetic susceptibility; 3) environmental and pathogen triggers; and 4) the skewed sex ratio of patients. It also suggests new avenues for treatment.

Effects of electronegative VLDL on endothelium damage in metabolic syndrome

OBJECTIVE

Biochemical heterogeneity governs functional disparities among lipoproteins. We examined charge-defined VLDL subfractions in metabolic syndrome (MetS) to determine whether their increased electronegativity is associated with increased cytotoxicity and whether high concentrations of highly electronegative subfractions render VLDL harmful to the vascular endothelium.

RESEARCH DESIGN AND METHODS

Plasma VLDL of normal individuals (control subjects) (n = 13) and of those with MetS (n = 13) was resolved into subfractions with increasing negative charge (V1-V5) by anion-exchange chromatography. Human aortic endothelial cells were treated with V1-V5 or unfractionated VLDL.

RESULTS

Compared with the control subjects, individuals with MetS had a significantly higher percentage of V5 VLDL (V5/VLDL%) (34 ± 20 vs. 39 ± 11%, respectively; P < 0.05) and plasma V5 concentration ([V5]) (5.5 ± 4.4 vs. 15.2 ± 8.5 mg/dL, respectively; P < 0.001). Apolipoprotein (apo)B100 levels decreased and apoC levels increased from V1 to V5, indicating that V5 is apoC-rich VLDL. Regression analyses of all 26 individuals showed that [V5] was positively correlated with total cholesterol (P = 0.016), triglyceride (P < 0.000001), and V5/VLDL% (P = 0.002). Fasting plasma glucose, but not waist circumference, exhibited a positive trend (P = 0.058); plasma HDL cholesterol exhibited a weak inverse trend (P = 0.138). V5 (10 μg/mL) induced apoptosis in ~50% of endothelial cells in 24 h. V5 was the most rapidly (<15 min) internalized subfraction and induced the production of reactive oxygen species (ROS) in endothelial cells after 20 min. Unfractionated MetS VLDL, but not control VLDL, also induced ROS production and endothelial cell apoptosis.

CONCLUSIONS

In populations with increased risk of diabetes, the vascular endothelium is constantly exposed to VLDL that contains a high proportion of V5. The potential impact of V5-rich VLDL warrants further investigation.

VLDL hydrolysis by hepatic lipase regulates PPARδ transcriptional responses

BACKGROUND

PPARs (α,γ,δ) are a family of ligand-activated transcription factors that regulate energy balance, including lipid metabolism. Despite these critical functions, the integration between specific pathways of lipid metabolism and distinct PPAR responses remains obscure. Previous work has revealed that lipolytic pathways can activate PPARs. Whether hepatic lipase (HL), an enzyme that regulates VLDL and HDL catabolism, participates in PPAR responses is unknown.

METHODS/PRINCIPAL FINDINGS

Using PPAR ligand binding domain transactivation assays, we found that HL interacted with triglyceride-rich VLDL (>HDL≫LDL, IDL) to activate PPARδ preferentially over PPARα or PPARγ, an effect dependent on HL catalytic activity. In cell free ligand displacement assays, VLDL hydrolysis by HL activated PPARδ in a VLDL-concentration dependent manner. Extended further, VLDL stimulation of HL-expressing HUVECs and FAO hepatoma cells increased mRNA expression of canonical PPARδ target genes, including adipocyte differentiation related protein (ADRP), angiopoietin like protein 4 and pyruvate dehydrogenase kinase-4. HL/VLDL regulated ADRP through a PPRE in the promoter region of this gene. In vivo, adenoviral-mediated hepatic HL expression in C57BL/6 mice increased hepatic ADRP mRNA levels by 30%. In ob/ob mice, a model with higher triglycerides than C57BL/6 mice, HL overexpression increased ADRP expression by 70%, demonstrating the importance of triglyceride substrate for HL-mediated PPARδ activation. Global metabolite profiling identified HL/VLDL released fatty acids including oleic acid and palmitoleic acid that were capable of recapitulating PPARδ activation and ADRP gene regulation in vitro.

CONCLUSIONS

These data define a novel pathway involving HL hydrolysis of VLDL that activates PPARδ through generation of specific monounsaturated fatty acids. These data also demonstrate how integrating cell biology with metabolomic approaches provides insight into specific lipid mediators and pathways of lipid metabolism that regulate transcription.