Triglyceride Storage Research Articles

Adrenoceptors in white, brown, and brite adipocytes.

Adrenoceptors play an important role in adipose tissue biology and physiology that includes regulating the synthesis and storage of triglycerides (lipogenesis), the breakdown of stored triglycerides (lipolysis), thermogenesis (heat production), glucose metabolism, and the secretion of adipocyte-derived hormones that can control whole-body energy homeostasis. These processes are regulated by the sympathetic nervous system through actions at different adrenoceptor subtypes expressed in adipose tissue depots. In this review, we have highlighted the role of adrenoceptor subtypes in white, brown, and brite adipocytes in both rodents and humans and have included detailed analysis of adrenoceptor expression in human adipose tissue and clonally derived adipocytes. We discuss important considerations when investigating adrenoceptor function in adipose tissue or adipocytes. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

Glycerolipid intermediates as signaling mediators in physiology and disease

Lipids have a number of essential biological roles that, despite a wealth of knowledge, somehow remain understudied. Glycerolipids are a major form of stored energy, play important structural functions as hydrophobic components of cell membranes, and have dynamic effects on signaling mediators within the cell and to distant tissues. Generally, it was believed that the pathways that synthesized lipids for these functions were distinct, compartmentalized, and did not widely intersect. For example, the main pathways for triglyceride storage as an energy source were not thought to play major roles in regulating the synthesis of lipids for signaling cascades even though many intermediates play roles as activators of intracellular kinases. However, it is now better appreciated that some of these storage intermediates also have signaling functions. In most cells, a pathway utilizing glycerol‐3‐phosphate as its initial substrate is the major route of triglyceride synthesis. Glycerol‐3‐phosphate undergoes two sequential acylations and then is dephosphorylated by lipin proteins to form diacylglycerol. Modulating the activity of lipin 1, a phosphatidic acid phosphohydrolase, has profound effects on skeletal muscle, adipose tissue, cardiac, and hepatic signaling by regulating the cellular abundance of phosphatidic acid. Evidence will be presented that lipin 1‐mediated signaling effects regulate metabolic flux, mitochondrial homeostasis, autophagy, cardiac and skeletal myocyte function, and impact cell death processes. These studies demonstrate that lipin 1 mediated effects on the concentrations of these intermediates are not important for storing energy, but also impact critical signaling cascades that control cellular homeostasis.Support or Funding InformationSupported by NIH grants R01 HL119225 and R01 DK78187This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Preservation of Acyl Coenzyme A Attenuates Pathological and Metabolic Cardiac Remodeling Through Selective Lipid Trafficking.

Metabolic remodeling in heart failure contributes to dysfunctional lipid trafficking and lipotoxicity. Acyl coenzyme A synthetase-1 (ACSL1) facilitates long-chain fatty acid (LCFA) uptake and activation with coenzyme A (CoA), mediating the fate of LCFA. The authors tested whether cardiac ACSL1 overexpression aids LCFA oxidation and reduces lipotoxicity under pathological stress of transverse aortic constriction (TAC). Mice with cardiac restricted ACSL1 overexpression (MHC-ACSL1) underwent TAC or sham surgery followed by serial in vivo echocardiography for 14 weeks. At the decompensated stage of hypertrophy, isolated hearts were perfused with 13C LCFA during dynamic-mode 13C nuclear magnetic resonance followed by in vitro nuclear magnetic resonance and mass spectrometry analysis to assess intramyocardial lipid trafficking. In parallel, acyl CoA was measured in tissue obtained from heart failure patients pre- and postleft ventricular device implantation plus matched controls. TAC-induced cardiac hypertrophy and dysfunction was mitigated in MHC-ACSL1 hearts compared with nontransgenic hearts. At 14 weeks, TAC increased heart weight to tibia length by 46% in nontransgenic mice, but only 26% in MHC-ACSL1 mice, whereas ACSL1 mice retained greater ejection fraction (ACSL1 TAC: 65.8±7.5%; nontransgenic TAC: 45.9±7.3) and improvement in diastolic E/E'. Functional improvements were mediated by ACSL1 changes to cardiac LCFA trafficking. ACSL1 accelerated LCFA uptake, preventing C16 acyl CoA loss post-TAC. Long-chain acyl CoA was similarly reduced in human failing myocardium and restored to control levels by mechanical unloading. ACSL1 trafficked LCFA into ceramides without normalizing the reduced triglyceride storage in TAC. ACSL1 prevented de novo synthesis of cardiotoxic C16- and C24-, and C24:1 ceramides and increased potentially cardioprotective C20- and C22-ceramides post-TAC. ACLS1 overexpression activated AMP activated protein kinase at baseline, but during TAC, prevented the reduced LCFA oxidation in hypertrophic hearts and normalized energy state (phosphocreatine:ATP) and consequently, AMP activated protein kinase activation. This is the first demonstration of reduced acyl CoA in failing hearts of humans and mice, and suggests possible mechanisms for maintaining mitochondrial oxidative energy metabolism by restoring long-chain acyl CoA through ASCL1 activation and mechanical unloading. By mitigating cardiac lipotoxicity, via redirected LCFA trafficking to ceramides, and restoring acyl CoA, ACSL1 delayed progressive cardiac remodeling and failure.

A high-fat diet impacts memory and gene expression of the head in mated female Drosophila melanogaster.

Obesity predisposes humans to a range of life-threatening comorbidities, including type 2 diabetes and cardiovascular disease. Obesity also aggravates neural pathologies, such as Alzheimer's disease, but this class of comorbidity is less understood. When Drosophila melanogaster (flies) are exposed to high-fat diet (HFD) by supplementing a standard medium with coconut oil, they adopt an obese phenotype of decreased lifespan, increased triglyceride storage, and hindered climbing ability. The latter development has been previously regarded as a potential indicator of neurological decline in fly models of neurodegenerative disease. Our objective was to establish the obesity phenotype in Drosophila and identify a potential correlation, if any, between obesity and neurological decline through behavioral assays and geneexpression microarray. We found that mated female w1118 flies exposed to HFD maintained an obese phenotype throughout adult life starting at 7 days, evidenced by increased triglyceride stores, diminished life span, and impeded climbing ability. While climbing ability worsened cumulativelybetween 7 and 14 days of exposure to HFD, there was no corresponding alteration in triglyceride content. Microarray analysis of the mated female w1118 fly head revealed HFD-induced changes in expression of genes with functions in memory, metabolism, olfaction, mitosis, cell signaling, and motor function. Meanwhile, an Aversive Phototaxis Suppression assay in mated female flies indicated reduced ability to recall an entrained memory 6 h after training. Overall, our results support the suitability of mated female flies for examining connections between diet-induced obesity and nervous or neurobehavioral pathology, and provide many directions for further investigation.

Obesity-associated inflammation triggers an autophagy\u2013lysosomal response in adipocytes and causes degradation of perilipin 1

In obesity, adipocytes exhibit high metabolic activity accompanied by an increase in lipid mobilization. Recent findings indicate that autophagy plays an important role in metabolic homeostasis. However, the role of this process in adipocytes remains controversial. Therefore, we performed an overall analysis of the expression profiles of 322 lysosomal/autophagic genes in the omental adipose tissue of lean and obese individuals, and found that among 35 significantly differentially expressed genes, 34 genes were upregulated. A large number of lysosomal/autophagic genes also were upregulated in murine 3T3-L1 adipocytes challenged with tumor necrosis factor α (TNFα) (within 24 h), which is in accordance with increased autophagy flux in adipocytes. SQSTM1/p62, a selective autophagy receptor that recognizes and binds specifically to ubiquitinated proteins, is transcriptionally upregulated upon TNFα stimulation as well. Perilipin 1 (PLIN1), a crucial lipid droplet protein, can be ubiquitinated and interacts with SQSTM1 directly. Thus, TNFα-induced autophagy is a more selective process that signals through SQSTM1 and can selectively degrade PLIN1. Our study indicates that local proinflammatory cytokines in obese adipose tissue impair triglyceride storage via autophagy induction.

Sex-based differences in hepatic and skeletal muscle triglyceride storage and metabolism 1.

Women and men store lipid differently within the body with men storing more fat in the android region and women storing more fat in the gynoid region. Fat is predominately stored in adipose tissue as triacylglycerides (TG); however, TG are also stored in other tissues including the liver and skeletal muscle. Excess hepatic TG storage, defined as a TG concentration >5% of liver weight and known as nonalcoholic fatty liver disease (NAFLD), is related to the metabolic syndrome. Similarly, elevated skeletal muscle TG, termed intramyocellular lipids (IMCL), are related to insulin resistance in obesity and type II diabetes. Men store more hepatic TG than women and, unsurprisingly, NAFLD is more prevalent in men than women. Women store more IMCL than men, yet type II diabetes risk is not greater, which is likely due to the manner in which women store TG within muscle. Sex-based differences in TG storage between men and women are underpinned by differences in messenger RNA expression, protein content, and enzyme activities of skeletal muscle and hepatic lipid metabolic pathways. Furthermore, women have a greater reliance on lipid during exercise because of upregulation of lipid oxidative pathways. The purpose of this review is to discuss the role of sex in mediating lipid storage and metabolism within skeletal muscle and the liver at rest and during exercise and its relationship with metabolic disease.

Obesity-induced activation of JunD promotes myocardial lipid accumulation and metabolic cardiomyopathy.

Metabolic cardiomyopathy (MC)-characterized by intra-myocardial triglyceride (TG) accumulation and lipotoxic damage-is an emerging cause of heart failure in obese patients. Yet, its mechanisms remain poorly understood. The Activator Protein 1 (AP-1) member JunD was recently identified as a key modulator of hepatic lipid metabolism in obese mice. The present study investigates the role of JunD in obesity-induced MC. JunD transcriptional activity was increased in hearts from diet-induced obese (DIO) mice and was associated with myocardial TG accumulation and left ventricular (LV) dysfunction. Obese mice lacking JunD were protected against MC. In DIO hearts, JunD directly binds PPARγ promoter thus enabling transcription of genes involved in TG synthesis, uptake, hydrolysis, and storage (i.e. Fas, Cd36, Lpl, Plin5). Cardiac-specific overexpression of JunD in lean mice led to PPARγ activation, cardiac steatosis, and dysfunction, thereby mimicking the MC phenotype. In DIO hearts as well as in neonatal rat ventricular myocytes exposed to palmitic acid, Ago2 immunoprecipitation, and luciferase assays revealed JunD as a direct target of miR-494-3p. Indeed, miR-494-3p was down-regulated in hearts from obese mice, while its overexpression prevented lipotoxic damage by suppressing JunD/PPARγ signalling. JunD and miR-494-3p were also dysregulated in myocardial specimens from obese patients as compared with non-obese controls, and correlated with myocardial TG content, expression of PPARγ-dependent genes, and echocardiographic indices of LV dysfunction. miR-494-3p/JunD is a novel molecular axis involved in obesity-related MC. These results pave the way for approaches to prevent or treat LV dysfunction in obese patients.

The Role of PCSK9 in the Pathogenesis of Non-alcoholic Fatty Liver Disease and the Effect of PCSK9 Inhibitors.

Statin treatment exhibits a beneficial effect on non-alcoholic fatty liver disease (NAFLD) and on cardiovascular disease (CVD) in patients with NAFLD. The aim of this review is to summarize the role of proprotein convertase subtilisin kexin type- 9(PCSK9) in the pathogenesis of NAFLD and discuss the effects of the new hypolipidaemic drugs PCSK9 inhibitors on NAFLD. Data indicates that high intrahepatic or circulating PCSK9 levels increase muscle and liver lipid storage, adipose energy storage and hepatic fatty acids, as well as triglycerides storage and secretion, thus contributing to the pathogenesis of NAFLD. The findings of animal and human studies, aiming to reduce PCSK9 with inhibitors (human IGG antibodies, antisense particles against PCSK9 mRNA, and small anti PCSK9 antibodies) point towards liver protection from NAFLD through inhibition of PCSK9 expression in the induction of degradation of hepatic HNF1a protein, insulin resistance (IR), and other mechanisms. The use of PCSK9 inhibitors ameliorates NAFLD, aside from beneficial effects on CVD and independently of low density lipoprotein cholesterol level reduction.

Immune challenge-induced oxidative damage may be mitigated by biliverdin.

An effective immune response results in the elimination of pathogens, but this immunological benefit may be accompanied by increased levels of oxidative damage. However, organisms have evolved mechanisms to mitigate the extent of such oxidative damage, including the production and mobilization of antioxidants. One potential mechanism of mitigating immune challenge-induced changes in oxidative physiology is increasing biliverdin production. Biliverdin is chemically an antioxidant, but within-tissue correlations between biliverdin concentration and oxidative damage have never been directly examined. To test how biliverdin tissue concentrations are associated with physiological responses to an immune challenge, we exposed northern bobwhite quail (Colinus virginianus) to one of four treatments: injection of a non-pathogenic antigen - either lipopolysaccharide or phytohemagglutinin, control injection of phosphate-buffered saline or a sham procedure with no injection. Twenty-four hours later, we quantified oxidative damage and triglyceride concentration in the plasma, and biliverdin concentration in the plasma, liver and spleen. We found that both types of immune challenge increased oxidative damage relative to both non-injected and vehicle-injected controls, but treatment had no effects on any other metric. However, across all birds, oxidative damage and biliverdin concentration in the plasma were negatively correlated, which is consistent with a localized antioxidant function of biliverdin. Additionally, we uncovered multiple links between biliverdin concentration, change in mass during the immune challenges and triglyceride levels, suggesting that pathways associated with biliverdin production may also be associated with aspects of nutrient mobilization. Future experiments that manipulate biliverdin levels or oxidative damage directly could establish a systemic antioxidant function or elucidate important physiological impacts on body mass maintenance and triglyceride storage, mobilization or transport.

Detection and Quantification of Lipid Droplets in Differentiated Human Podocytes.

Lipid droplets (LDs) are dynamic organelles that regulate the storage and homeostasis of intracellular triglycerides and other neutral lipids. Studies show that the number, morphology, and subcellular localization of LDs are altered in a growing number of diseases. As such, methodologies for imaging and quantifying LDs have become essential tools for detecting changes in cellular lipid metabolism, which could be an important indicator of disease onset or progression. We previously reported on the accumulation of LDs in podocytes of the kidney glomerulus in nephrological diseases of metabolic and non-metabolic origin. Here, we describe a high-content analysis (HCA) method for automated detection and quantification of LDs in differentiated human podocytes.

Utilization of Waste Cooking Oil and Tallow for Production of Toilet “Bath” Soap.

A green prospective based on the reuse of waste materials such as beef tallow and waste cooking vegetable oils to manufacture soap is presented. Beef tallow and waste cooking oils that is discarded as waste from households and restaurants after frying is reviewed for the production of toilet (bath) soap. The discarded oil is purified with a brine solution and bleached with Hydrogen Peroxide (H2O2.) Purified waste cooking oils and beef tallow is mixed with coconut oil commonly used oil in toilet soap manufacturing. The oils are normally mixed at different ratios for the preparation of toilet soap. The triglycerides in the vegetable oils and beef tallow are saponified with Sodium Hydroxide (NaOH) by hydrolysis. Cold process soap shows significant improvements in physical properties at different triglycerides ratios and storage time at room temperature. It could be recommended that discarded waste cooking vegetable oils can be used after purification and bleaching together with beef tallow that may be regarded as waste to produce toilet (bath) soaps.

Epicardial Adipose Tissue in Cardiovascular Disease.

Cardiovascular disease (CVD) is the main cause of morbidity and mortality in industrialized countries, despite the evolution of treatments and revascularization strategies. Obesity, also accompanied by a chronic inflammatory process, is an independent risk factor for CVD. Abdominal adipose tissue is a complex, metabolically very active organ capable of producing different adipokines and hormones, responsible for endocrine-metabolic comorbidities. The epicardial adipose tissue (EAT) has not been as extensively studied as the abdominal or subcutaneous adipose tissue. However, recent evidence associates it with an increased cardiometabolic risk due to its apposition with the heart. EAT stores triglycerides to provide energy to the myocardium and is characterized by its greater ability to release and capture free fatty acids. EAT strategic localization allows a singular cross talk with cardiomyocytes and vascular wall cells. The fact that EAT produces pro-inflammatory adipokines as well as metalloproteinases and pro-oxidant substances, highlights its possible direct impact on plaque vulnerability and heart failure, being still necessary further studies of EAT behavior in CVD.

Random Forest Analysis of Untargeted Metabolomics Data Suggests Increased Use of Omega Fatty Acid Oxidation Pathway in Drosophila Melanogaster Larvae Fed a Medium Chain Fatty Acid Rich High-Fat Diet.

Obesity is a complex disease, shaped by both genetic and environmental factors such as diet. In this study, we use untargeted metabolomics and Drosophila melanogaster to model how diet and genotype shape the metabolome of obese phenotypes. We used 16 distinct outbred genotypes of Drosophila larvae raised on normal (ND) and high-fat (HFD) diets, to produce three distinct phenotypic classes; genotypes that stored more triglycerides on a ND relative to the HFD, genotypes that stored more triglycerides on a HFD relative to ND, and genotypes that showed no change in triglyceride storage on either of the two diets. Using untargeted metabolomics we characterized 350 metabolites: 270 with definitive chemical IDs and 80 that were chemically unidentified. Using random forests, we determined metabolites that were important in discriminating between the HFD and ND larvae as well as between the triglyceride phenotypic classes. We found that flies fed on a HFD showed evidence of an increased use of omega fatty acid oxidation pathway, an alternative to the more commonly used beta fatty acid oxidation pathway. Additionally, we observed no correlation between the triglyceride storage phenotype and free fatty acid levels (laurate, caprate, caprylate, caproate), indicating that the distinct metabolic profile of fatty acids in high-fat diet fed Drosophila larvae does not propagate into triglyceride storage differences. However, dipeptides did show moderate differences between the phenotypic classes. We fit Gaussian graphical models (GGMs) of the metabolic profiles for HFD and ND flies to characterize changes in metabolic network structure between the two diets, finding the HFD to have a greater number of edges indicating that metabolome varies more across samples on a HFD. Taken together, these results show that, in the context of obesity, metabolomic profiles under distinct dietary conditions may not be reliable predictors of phenotypic outcomes in a genetically diverse population.

Apple Pomace Consumption Favorably Alters Hepatic Lipid Metabolism in Young Female Sprague-Dawley Rats Fed a Western Diet.

Apple pomace, which is a waste byproduct of processing, is rich in several nutrients, particularly dietary fiber, indicating potential benefits for diseases that are attributed to poor diets, such as non-alcoholic fatty liver disease (NAFLD). NAFLD affects over 25% of United States population and is increasing in children. Increasing fruit consumption can influence NAFLD. The study objective was to replace calories in standard or Western diets with apple pomace to determine the effects on genes regulating hepatic lipid metabolism and on risk of NAFLD. Female Sprague-Dawley rats were randomly assigned (n = 8 rats/group) to isocaloric diets of AIN-93G and AIN-93G/10% w/w apple pomace (AIN/AP) or isocaloric diets of Western (45% fat, 33% sucrose) and Western/10% w/w apple pomace (Western/AP) diets for eight weeks. There were no significant effects on hepatic lipid metabolism in rats fed AIN/AP. Western/AP diet containing fiber-rich apple pomace attenuated fat vacuole infiltration, elevated monounsaturated fatty acid content, and triglyceride storage in the liver due to higher circulating bile and upregulated hepatic DGAT2 gene expression induced by feeding a Western diet. The study results showed the replacement of calories in Western diet with apple pomace attenuated NAFLD risk. Therefore, apple pomace has the potential to be developed into a sustainable functional food for human consumption.

Oleate increase neutral lipid accumulation, cellular respiration and rescues palmitate-exposed GLP-1 secreting cells by reducing ceramide-induced ROS

BackgroundFatty acids (FAs), and especially monounsaturated FAs (MUFAs) stimulate GLP-1 release. However, lipotoxicity is indicated in GLP-1 secreting cells following long-term exposure to elevated levels of saturated FAs (SFAs) in vivo and in vitro, where in vitro studies indicate that cosupplementation with MUFAs confers lipoprotection. SFAs and MUFAs differentially affect the fate of cells in ways that depend on the cell type, concentration and ratio of the FAs. The present study was designed to further elucidate the mechanisms underlying the effects of SFAs/MUFAs on GLP-1-producing cells in terms of lipotoxicity/lipoprotection and GLP-1 secretion. MethodsCultured GLP-1 secreting cells were exposed to hyperlipidemia simulated by SFA-albumin complexes where the molar ratio was 2:1. The cellular response to simulated hyperlipidemia was assessed in the presence/absence of MUFA cosupplementation by determining intracellular ceramide, ROS, neutral lipid accumulation, and cellular respiration. The role for cellular respiration in GLP-1 secretion in response to SFAs/MUFAs was assessed. ResultsGeneration of intracellular ceramide mediate a detrimental increased in ROS production following long term exposure to SFAs in GLP-1-secreting cells. Cosupplementation with MUFAs increases cellular respiration, triglyceride synthesis, and the expression of ceramide kinase, while reducing ceramide synthesis and attenuating ROS production, caspase-3 activity and DNA fragmentation. Further, acute secretory effects of unsaturated FAs are independent of FAO, but mediated by a FFAR1 induced increase in cellular respiration. ConclusionThis study demonstrates novel data supporting effects of MUFAs on the ceramide biosynthetic pathway, triglyceride storage respiration and secretion in GLP-1 secreting cells. These findings may be of value for nutritional interventions, as well as for identification of novel targets, to help preserve L-cell mass and potentiate GLP-1 secretion in diabesity.

MicroRNA-124 Regulates Fatty Acid and Triglyceride Homeostasis

SummaryMicroRNAs (miRNAs) are part of a complex regulatory network that modulates cellular lipid metabolism. Here, we identify miR-124 as a regulator of triglyceride (TG) metabolism. This study advances our knowledge of the role of miR-124 in human hepatoma cells. Transcriptional profiling of Huh7.5 cells overexpressing miR-124 reveals enrichment for host factors involved in fatty acid oxidation among repressed miRNA targets. In addition, miR-124 down-regulates arylacetamide deacetylase (AADAC) and adipose triglyceride lipase, lipases proposed to mediate breakdown of hepatic TG stores for lipoprotein assembly and mitochondrial β-oxidation. Consistent with the inhibition of TG and fatty acid catabolism, miR-124 expression promotes cellular TG accumulation. Interestingly, miR-124 inhibits the production of hepatitis C virus, a virus that hijacks lipid pathways during its life cycle. Antiviral activity of miR-124 is consistent with repression of AADAC, a pro-viral host factor. Overall, our data highlight miR-124 as a novel regulator of TG metabolism in human hepatoma cells.

Phenotypic Modulation of Skeletal Muscle Fibers in LPIN1-Deficient Lipodystrophic ( fld) Mice.

Lipin-1 ( Lpin1)-deficient lipodystrophic mice have scant and immature adipocytes and develop transient fatty liver early in life. Unlike normal mice, these mice cannot rely on stored triglycerides to generate adenosine triphosphate (ATP) from the β-oxidation of fatty acids during periods of fasting. To compensate, these mice store much higher amounts of glycogen in skeletal muscle and liver than wild-type mice in order to support energy needs during periods of fasting. Our studies demonstrated that there are phenotypic changes in skeletal muscle fibers that reflect an adaptation to this unique metabolic situation. The phenotype of skeletal muscle (soleus, gastrocnemius, plantaris, and extensor digitorum longus [EDL]) from Lpin1-/- was evaluated using various methods including immunohistochemistry for myosin heavy chains (Myh) 1, 2, 2a, 2b, and 2x; enzyme histochemistry for myosin ATPase, cytochrome-c oxidase (COX), and succinyl dehydrogenase (SDH); periodic acid-Schiff; and transmission electron microscopy. Fiber-type changes in the soleus muscle of Lpin1-/- mice were prominent and included decreased Myh1 expression with concomitant increases in Myh2 expression and myosin-ATPase activity; this change was associated with an increase in the presence of Myh1/2a or Myh1/2x hybrid fibers. Alterations in mitochondrial enzyme activity (COX and SDH) were apparent in the myofibers in the soleus, gastrocnemius, plantaris, and EDL muscles. Electron microscopy revealed increases in the subsarcolemmal mitochondrial mass in the muscles of Lpin1-/- mice. These data demonstrate that lipin-1 deficiency results in phenotypic fiber-specific modulation of skeletal muscle necessary for compensatory fuel utilization adaptations in lipodystrophy.

Increased Reticulon 3 (RTN3) Leads to Obesity and Hypertriglyceridemia by Interacting With Heat Shock Protein Family A (Hsp70) Member 5 (HSPA5).

Reticulon 3 (RTN3) is an endoplasmic reticulum protein that has previously been shown to play a role in neurodegenerative diseases, but little is known about its role in lipid metabolism. Obese patients (n=149), hypertriglyceridemic patients (n=343), and healthy control subjects (n=84) were enrolled to assess their levels of RTN3. To explore the pathophysiological roles of RTN3 in the control of lipid metabolism, we used transgenic mice overexpressing the wild-type human RTN3 gene, the RTN3-null transgenic mouse model, and multiple Caenorhabditis legans strains for molecular characterization. The underlying mechanisms were studied with 3T3L1 cell cultures in vitro. We report that overexpressed RTN3 in mice induces obesity and higher accumulation of triglycerides. Increased RTN3 expression is also found in patients with obesity and hypertriglyceridemia. We reveal that RTN3 plays critical roles in regulating the biosynthesis and storage of triglycerides and in controlling lipid droplet expansion. Mechanistically, RTN3 regulates these events through its interactions with heat shock protein family A (Hsp70) member 5, and this enhanced interaction increases sterol regulatory element-binding protein 1c and AMP-activated kinase activity. This study provides evidence for a role of RTN3 in inducing obesity and triglyceride accumulation and suggests that inhibiting the expression of RTN3 in fat tissue may be a novel therapeutic approach to treat obesity and hypertriglyceridemia.

Determination of optimum carcass weight for meat quality and fatty acid composition in fat-tailed male and female Chall lambs

The aim of this study was to determine the optimum carcass weight for meat quality and fatty acid composition in fat-tailed Chall lambs. Thirty lambs (15 male and 15 female) were allotted to three carcass weight groups: (1) light carcass weight (LCW 10-15kg), (2) moderate carcass weight (MCW 15-20kg), and (3) heavy carcass weight (HCW 20-25kg). Back fat thickness and intramuscular fat (IMF) content were greater (P < 0.05) for HCW and female groups than their counterparts, respectively. Drip loss was lower (P < 0.05) for female and HCW lamb groups than male and LCW group, respectively. Female and LCW lambs had lower (P < 0.05) shear force compared with their corresponding male and HCW groups. Meat from LCW and MCW lambs had higher lightness (L* value; 43.6, 43.5 vs. 39.9), while redness (a* value; 13.6, 13.9 vs. 15.4) was greater for HCW and female (13.7 vs. 14.9) lambs compared with their counterparts (P < 0.05). The MCW lambs produced meat with higher overall acceptability compared with other two groups (P < 0.05). The HCW lambs contained lower polyunsaturated fatty acids (PUFA), polyunsaturated fatty acids to saturated fatty acids (P:S) ratio, and n-3 PUFA compared with LCW group (P < 0.05). Results show that as the animal grow faster and achieved HCW, the IMF content also increased mainly as storage triglyceride, while functional fats consisting long-chain omega-3 did not increase proportionately. In addition, the study also demonstrates that using IMF for predicting or assessing meat quality aspects such as juiciness and flavor or the nutritional value of meat relating to health claimable fatty acids would not be appropriate.

Phosphatidylcholine synthesis regulates triglyceride storage and chylomicron secretion by Caco2 cells

Intracellular lipid droplets (LDs) supply fatty acids for energy, membrane biogenesis, and lipoprotein secretion. The surface monolayer of LDs is composed of phospholipids, primarily phosphatidylcholine (PC), that stabilize the neutral lipid core of triglyceride (TG). To determine the relationship between PC synthesis and TG storage and secretion in chylomicrons, we used a model of intestinal-derived human epithelial colorectal adenocarcinoma (Caco2) cells with knockout of PCYT1A, which encodes the rate-limiting enzyme CTP:phosphocholine cytidylyltransferase (CCT)α in the CDP-choline pathway, that were treated with the fatty acid oleate. CRISPR/Cas9 knockout of CCTα in Caco2 cells (Caco2-KO cells) reduced PC synthesis by 50%. Compared with Caco2 cells, Caco2-KO cells exposed to oleate had fewer and larger LDs and greater TG accumulation as a result. The addition of exogenous lysophosphatidylcholine to Caco2-KO cells reversed the LD morphology defect. Caco2-KO cells, differentiated into epithelial monolayers, accumulated intracellular TG and had deficient TG and chylomicron-associated apoB48 secretion; apoB100 secretion was unaffected by CCTα knockout or oleate. Metabolic-labeling and LD imaging of Caco2-KO cells indicated preferential shuttling of de novo synthesized TG into larger LDs rather than into chylomicrons. Thus, reduced de novo PC synthesis in Caco2 cells enhances TG storage in large LDs and inhibits apoB48 chylomicron secretion.