Adipose triglyceride lipase-mediated lipolysis of cellular fat stores is activated by CGI-58 and defective in Chanarin-Dorfman Syndrome

The Lipolysome-A Highly Complex and Dynamic Protein Network Orchestrating Cytoplasmic Triacylglycerol Degradation

The catabolism of intracellular triacylglycerols (TAGs) involves the activity of cytoplasmic and lysosomal enzymes. Cytoplasmic TAG hydrolysis, commonly termed lipolysis, is catalyzed by the sequential action of three major hydrolases, namely adipose triglyceride lipase, hormone-sensitive lipase, and monoacylglycerol lipase. All three enzymes interact with numerous protein binding partners that modulate their activity, cellular localization, or stability. Deficiencies of these auxiliary proteins can lead to derangements in neutral lipid metabolism and energy homeostasis. In this review, we summarize the composition and the dynamics of the complex lipolytic machinery we like to call "lipolysome".

Rab7 controls lipid droplet-phagosome association during mycobacterial infection

Lipid droplets (LDs) are organelles that have multiple roles in inflammatory and infectious diseases. LD act as essential platforms for immunometabolic regulation, including as sites for lipid storage and metabolism, inflammatory lipid mediator production, and signaling pathway compartmentalization. Accumulating evidence indicates that intracellular pathogens may exploit host LDs as source of nutrients and as part of their strategy to promote immune evasion. Notably, numerous studies have demonstrated the interaction between LDs and pathogen-containing phagosomes. However, the mechanism involved in this phenomenon remains elusive. Here, we observed LDs and PLIN2 surrounding M. bovis BCG-containing phagosomes, which included observations of a bacillus cell surrounded by lipid content inside a phagosome and LAM from mycobacteria co-localizing with LDs; these results were suggestive of exchange of contents between these compartments. By using beads coated with M.tb lipids, we demonstrated that LD-phagosome associations are regulated through the mycobacterial cell wall components LAM and PIM. In addition, we demonstrated that Rab7 and RILP, but not Rab5, localizes to LDs of infected macrophages and observed the presence of Rab7 at the site of interaction with an infected phagosome. Moreover, treatment of macrophages with the Rab7 inhibitor CID1067700 significantly inhibited the association between LDs and LAM-coated beads. Altogether, our data demonstrate that LD-phagosome interactions are controlled by mycobacterial cell wall components and Rab7, which enables the exchange of contents between LDs and phagosomes and may represent a fundamental aspect of bacterial pathogenesis and immune evasion.

The omentum of obese girls harbors small adipocytes and browning transcripts

Severe obesity (SO) affects about 6% of youth in the United States, augmenting the risks for cardiovascular disease and type 2 diabetes. Herein, we obtained paired omental adipose tissue (omVAT) and abdominal subcutaneous adipose tissue (SAT) biopsies from girls with SO undergoing sleeve gastrectomy (SG), to test whether differences in cellular and transcriptomic profiles between omVAT and SAT depots affect insulin sensitivity differently. Following weight loss, these analyses were repeated in a subgroup of subjects having a second SAT biopsy. We found that omVAT displayed smaller adipocytes compared with SAT, increased lipolysis through adipose triglyceride lipase phosphorylation, reduced inflammation, and increased expression of browning/beiging markers. Contrary to omVAT, SAT adipocyte diameter correlated with insulin resistance. Following SG, both weight and insulin sensitivity improved markedly in all subjects. SAT adipocytes' size became smaller, showing increased lipolysis through perilipin 1 phosphorylation, decreased inflammation, and increased expression in browning/beiging markers. In summary, in adolescent girls with SO, both omVAT and SAT depots showed distinct cellular and transcriptomic profiles. Following weight loss, the SAT depot changed its cellular morphology and transcriptomic profiles into more favorable ones. These changes in the SAT depot may play a fundamental role in the resolution of insulin resistance.

The Role of Adipose Triglyceride Lipase and Cytosolic Lipolysis in Cardiac Function and Heart Failure

Heart failure is one of the leading causes of death worldwide. New therapeutic concepts are urgently required to lower the burden of heart failure with reduced ejection fraction (HFrEF) and heart failure with preserved ejection fraction (HFpEF), the two major forms of heart failure. Lipolytic processes are induced during the development of heart failure and occur in adipose tissue and multiple organs, including the heart. Increasing evidence suggests that cellular lipolysis, in particular, adipose triglyceride lipase (ATGL) activity, has an important function in cardiac (patho)physiology. This review summarizes the crucial role of cellular lipolysis for normal cardiac function and for the development of HFrEF and HFpEF. We discuss the most relevant pre-clinical studies and elaborate on the cardiac consequences of non-myocardial and myocardial lipolysis modulation. Finally, we critically analyze the therapeutic importance of pharmacological ATGL inhibition as a potential treatment option for HFrEF and/or HFpEF in the future.

Western diet induces severe nonalcoholic steatohepatitis, ductular reaction, and hepatic fibrosis in liver CGI-58 knockout mice

Humans and rodents with Comparative Gene Identification-58 (CGI-58) mutations manifest nonalcoholic fatty liver disease (NAFLD). Here we show that liver CGI-58 knockout (LivKO) mice fed a Western diet rapidly develop advanced NAFLD, including nonalcoholic steatohepatitis (NASH) and hepatic fibrosis. After 14 weeks of diet challenge, starting at 6 weeks of age, LivKO mice showed increased inflammatory cell infiltration and proinflammatory gene expression in the liver, which was associated with elevated plasma levels of aminotransferases. Hepatic ductular reactions, pericellular fibrosis, and bridging fibrosis were observed only in the LivKO mice. Consistently, the KO mice had a significant increase in hepatic mRNAs for fibrogenic genes. In addition, LivKO mice displayed massive accumulation of lipid droplets (LDs) in hepatocytes. LDs were also observed in the cholangiocytes of the LivKO mice, but not the floxed controls. Four of the five LD coat proteins, including perilipins 2, 3, 4, and 5, were increased in the CGI-58 KO liver. CRISPR/Cas9-mediated knockout of CGI-58 in Huh7 human hepatoma cells induced LD deposition and perilipin expression, suggesting a cell autonomous effect. Our findings establish the Western diet-fed LivKO mice as an animal model of NASH and hepatic fibrosis. These animals may facilitate preclinical screening of therapeutic agents that counter against NAFLD progression.

The effects of growth hormone on adipose tissue: old observations, new mechanisms

The ability of growth hormone (GH) to induce adipose tissue lipolysis has been known for over five decades; however, the molecular mechanisms that mediate this effect and the ability of GH to inhibit insulin-stimulated glucose uptake have scarcely been documented. In this same time frame, our understanding of adipose tissue has evolved to reveal a complex structure with distinct types of adipocyte, depot-specific differences, a biologically significant extracellular matrix and important endocrine properties mediated by adipokines. All these aforementioned features, in turn, can influence lipolysis. In this Review, we provide a historical and current overview of the lipolytic effect of GH in humans, mice and cultured cells. More globally, we explain lipolysis in terms of GH-induced intracellular signalling and its effect on obesity, insulin resistance and lipotoxicity. In this regard, findings that define molecular mechanisms by which GH induces lipolysis are described. Finally, data are presented for the differential effect of GH on specific adipose tissue depots and on distinct classes of metabolically active adipocytes. Together, these cellular, animal and human studies reveal novel cellular phenotypes and molecular pathways regulating the metabolic effects of GH on adipose tissue.

Spatiotemporal contact between peroxisomes and lipid droplets regulates fasting-induced lipolysis via PEX5

Lipid droplets (LDs) are key subcellular organelles for regulating lipid metabolism. Although several subcellular organelles participate in lipid metabolism, it remains elusive whether physical contacts between subcellular organelles and LDs might be involved in lipolysis upon nutritional deprivation. Here, we demonstrate that peroxisomes and peroxisomal protein PEX5 mediate fasting-induced lipolysis by stimulating adipose triglyceride lipase (ATGL) translocation onto LDs. During fasting, physical contacts between peroxisomes and LDs are increased by KIFC3-dependent movement of peroxisomes toward LDs, which facilitates spatial translocations of ATGL onto LDs. In addition, PEX5 could escort ATGL to contact points between peroxisomes and LDs in the presence of fasting cues. Moreover, in adipocyte-specific PEX5-knockout mice, the recruitment of ATGL onto LDs was defective and fasting-induced lipolysis is attenuated. Collectively, these data suggest that physical contacts between peroxisomes and LDs are required for spatiotemporal translocation of ATGL, which is escorted by PEX5 upon fasting, to maintain energy homeostasis.

Lipid droplets are organelles that regulate lipid metabolism but if organellar contacts play a role during lipolysis is unclear. Here, the authors show that peroxisomes and peroxisomal protein PEX5 play pivotal roles in the spatial and temporal regulation of fasting-induced lipolysis by translocating ATGL onto lipid droplets

The Gene and Protein Expression of the Main Components of the Lipolytic System in Human Myocardium and Heart Perivascular Adipose Tissue. Effect of Coronary Atherosclerosis

The aim of our study was to examine the regulation of triacylglycerols (TG) metabolism in myocardium and heart perivascular adipose tissue in coronary atherosclerosis. Adipose triglyceride lipase (ATGL) is the major TG-hydrolase. The enzyme is activated by a protein called comparative gene identification 58 (CGI-58) and inhibited by a protein called G0/G1 switch protein 2 (G0S2). Samples of the right atrial appendage and perivascular adipose tissue were obtained from two groups of patients: 1—with multivessel coronary artery disease qualified for coronary artery bypass grafting (CAD), 2—patients with no atherosclerosis qualified for a valve replacement (NCAD). The mRNA and protein analysis of ATGL, HSL, CGI-58, G0S2, FABP4, FAT/CD36, LPL, β-HAD, CS, COX4/1, FAS, SREBP-1c, GPAT1, COX-2, 15-LO, and NFκβ were determined by using real-time PCR and Western Blot. The level of lipids (i.e., TG, diacylglycerol (DG), and FFA) was examined by GLC. We demonstrated that in myocardium coronary atherosclerosis increases only the transcript level of G0S2 and FABP4. Most importantly, ATGL, β-HAD, and COX4/1 protein expression was reduced and it was accompanied by over double the elevation in TG content in the CAD group. The fatty acid synthesis and their cellular uptake were stable in the myocardium of patients with CAD. Additionally, the expression of proteins contributing to inflammation was increased in the myocardium of patients with coronary stenosis. Finally, in the perivascular adipose tissue, the mRNA of G0S2 was elevated, whereas the protein content of FABP-4 was increased and for COX4/1 diminished. These data suggest that a reduction in ATGL protein expression leads to myocardial steatosis in patients with CAD.

Progesterone Regulation of Milk Fat Globule Size Is VLDL Dependent

Progesterone plays a pivotal role during mammogenesis and serves as an inhibitor of the secretory activation of mammary cells in the last days of gestation. However, its role during lactogenesis, in particular its involvement in lipid metabolism, and milk fat content and composition, is unknown. Here, we provide new evidence of progesterone's involvement in the regulation of milk fat globule (MFG) synthesis and secretion. Findings from both in vivo and in vitro studies indicated that the concentration and the direction (increase vs. decrease) of progesterone concentration to which the mammary epithelial cells (MECs) are exposed affect MFG size. This was found to be very-low-density lipoprotein (VLDL) dependent: in the presence of VLDL, the proportion of MEC with small lipid droplets (<1 μm) increased 2.4-fold, and the proportion of large lipid droplets (>1 μm) increased 4-fold; in the absence of VLDL, no differences were found. The findings add to our understanding of the mechanism underlying the regulation of MFG size and provide new evidence for progesterone's role in lipid metabolism in the mammary gland during lactogenesis. The fact that the size, synthesis, and composition of MFG are affected by the cyclic pattern of progesterone concentration in the circulation might have physiologically relevant consequences, in particular on milk as a nutritional source.

Degradation of Lipid Droplets in Plants and Algae-Right Time, Many Paths, One Goal

In eukaryotic cells, lipids in the form of triacylglycerols (TAGs) are the major reservoir of cellular carbon and energy. These TAGs are packed into specialized organelles called lipid droplets (LDs). They can be found in most, if not all, types of cells, from bacteria to human. Recent data suggest that rather than being simple storage organelles, LDs are very dynamic structures at the center of cellular metabolism. This is also true in plants and algae, where LDs have been implicated in many processes including energy supply; membrane structure, function, trafficking; and signal transduction. Plant and algal LDs also play a vital role in human life, providing multiple sources of food and fuel. Thus, a lot of attention has been paid to metabolism and function of these organelles in recent years. This review summarizes the most recent advances on LDs degradation as a key process for TAGs release. While the initial knowledge on this process came from studies in oilseeds, the findings of the last decade revealed high complexity and specific mechanisms of LDs degradation in plants and algae. This includes identification of numerous novel proteins associated with LDs as well as a prominent role for autophagy in this process. This review outlines, systemizes, and discusses the most current data on LDs catabolism in plants and algae.

Anti-Lipolysis Induced by Insulin in Diverse Pathophysiologic Conditions of Adipose Tissue

As an important energy reservoir, adipose tissue maintains lipid balance and regulates energy metabolism. When the body requires energy, adipocytes provide fatty acids to peripheral tissues through lipolysis. Insulin plays an important role in regulating normal fatty acid levels by inhibiting lipolysis. When the morphology of adipose tissue is abnormal, its microenvironment changes and the lipid metabolic balance is disrupted, which seriously impairs insulin sensitivity. As the most sensitive organ to respond to insulin, lipolysis levels in adipose tissue are affected by impaired insulin function, which results in serious metabolic diseases. However, the specific underlying mechanisms of this process have not yet been fully elucidated, and further study is required. The purpose of this review is to discuss the effects of adipose tissue on the anti-lipolysis process triggered by insulin under different conditions. In particular, the functional changes of this process respond to inconsonantly morphological changes of adipose tissue.

CGI-58: Versatile Regulator of Intracellular Lipid Droplet Homeostasis

Comparative gene identification-58 (CGI-58), also known as α/β-hydrolase domain-containing 5 (ABHD5), is a member of a large family of proteins containing an α/β-hydrolase-fold. CGI-58 is well-known as the co-activator of adipose triglyceride lipase (ATGL), which is a key enzyme initiating cytosolic lipid droplet lipolysis. Mutations in either the human CGI-58 or ATGL gene cause an autosomal recessive neutral lipid storage disease, characterized by the excessive accumulation of triglyceride (TAG)-rich lipid droplets in the cytoplasm of almost all cell types. CGI-58, however, has ATGL-independent functions. Distinct phenotypes associated with CGI-58 deficiency commonly include ichthyosis (scaly dry skin), nonalcoholic steatohepatitis, and hepatic fibrosis. Through regulated interactions with multiple protein families, CGI-58 controls many metabolic and signaling pathways, such as lipid and glucose metabolism, energy balance, insulin signaling, inflammatory responses, and thermogenesis. Recent studies have shown that CGI-58 regulates the pathogenesis of common metabolic diseases in a tissue-specific manner. Future studies are needed to molecularly define ATGL-independent functions of CGI-58, including the newly identified serine protease activity of CGI-58. Elucidation of these versatile functions of CGI-58 may uncover fundamental cellular processes governing lipid and energy homeostasis, which may help develop novel approaches that counter against obesity and its associated metabolic sequelae.

S-petasin inhibits lipid accumulation in oleic acid-induced HepG2 cells through activation of the AMPK signaling pathway

S-petasin inhibits lipid accumulation in oleic acid-induced HepG2 cells.

RAB18 Loss Interferes With Lipid Droplet Catabolism and Provokes Autophagy Network Adaptations

Autophagy is dependent on appropriate lipid supply for autophagosome formation. The regulation of lipid acquisition and the autophagy network response to lipid-limiting conditions are mostly elusive. Here, we show that the knockout of the RAB GTPase RAB18 interferes with lipid droplet catabolism, causing an impaired fatty acid release. The resulting reduced lipid-droplet-derived lipid availability influences autophagy and provokes adaptive modifications of the autophagy network. These adjustments include increased expression and phosphorylation of ATG2B as well as augmented formation of the ATG12-ATG5 conjugate. Moreover, ATG9A shows an enhanced phosphorylation at amino acid residues tyrosine 8 and serine 14, resulting in an increased ATG9A trafficking. Via pharmacological inhibition of Y8 phosphorylation, we demonstrate that this ATG9A modification is important to maintain basal autophagy under RAB18 knockout conditions. However, while the network adaptations are sufficient to maintain basal autophagic activity, they are incapable of ensuring autophagy induction upon starvation, which is characterized by an enhanced lipid demand. Thus, here, we define the molecular role of RAB18 in connecting lipid droplets and autophagy, emphasize the significance of lipid droplets as lipid sources for the degradative pathway, and uncover a remarkable autophagy network plasticity, including phosphorylation-dependent ATG9A activation, to compensate reduced lipid availability in order to rescue basal autophagic activity.

PNPLA3-I148M: a problem of plenty in non-alcoholic fatty liver disease

Fatty liver disease (FLD) affects more than one-third of the population in the western world and an increasing number of children in the United States. It is a leading cause of obesity and liver transplantation. Mechanistic insights into the causes of FLD are urgently needed since no therapeutic intervention has proven to be effective. A sequence variation in patatin like phospholipase domain-containing protein 3 (PNPLA3), rs 738409, is strongly associated with the progression of fatty liver disease. The resulting mutant causes a substitution of isoleucine to methionine at position 148. The underlying mechanism of this disease remains unsolved although several studies have illuminated key insights into its pathogenesis. This review highlights the progress in our understanding of PNPLA3 function in lipid droplet dynamics and explores possible therapeutic interventions to ameliorate this human health hazard.

Genetically-encoded sensors to detect fatty acid production and trafficking

OBJECTIVE

Fatty acids are important for biological function; however, in excess, they can cause metabolic dysregulation. Methods to image and detect fatty acids in real time are lacking. Therefore, the current study examined the dynamics of fatty acid trafficking and signaling utilizing novel fluorescent and luminescent approaches.

METHODS

We generated fluorescent and luminescent-based genetically-encoded sensors based upon the ligand-dependent interaction between PPARα and SRC-1 to image and detect cellular dynamics of fatty acid trafficking.

RESULTS

The use of a fluorescent sensor demonstrates that fatty acids traffic rapidly from lipid droplets to the nucleus. Both major lipases ATGL and HSL contribute to fatty acid signaling from lipid droplet to nucleus, however, their dynamics differ. Furthermore, direct activation of lipolysis, independent of receptor-mediated signaling is sufficient to promote lipid droplet to nuclear trafficking of fatty acids. A luminescent-based sensor that reports intracellular fatty acid levels is amenable to high-throughput analysis.

CONCLUSIONS

Fatty acids traffic from lipid droplets to the nucleus within minutes of stimulated lipolysis. Genetically-encoded fluorescent and luminescent based sensors can be used to probe the dynamics of fatty acid trafficking and signaling.

The lipid droplet-associated protein ABHD5 protects the heart through proteolysis of HDAC4

Catecholamines stimulate the first step of lipolysis by PKA-dependent release of the lipid droplet-associated protein ABHD5 from perilipin to co-activate the lipase ATGL. Here, we unmask a yet unrecognized proteolytic and cardioprotective function of ABHD5. ABHD5 acts in vivo and in vitro as a serine protease cleaving HDAC4. Through the production of an N-terminal polypeptide of HDAC4 (HDAC4-NT), ABHD5 inhibits MEF2-dependent gene expression and thereby controls glucose handling. ABHD5-deficiency leads to neutral lipid storage disease in mice. Cardiac-specific gene therapy of HDAC4-NT does not protect from intra-cardiomyocyte lipid accumulation but strikingly from heart failure, thereby challenging the concept of lipotoxicity-induced heart failure. ABHD5 levels are reduced in failing human hearts and murine transgenic ABHD5 expression protects from pressure-overload induced heart failure. These findings represent a conceptual advance by connecting lipid with glucose metabolism through HDAC4 proteolysis and enable new translational approaches to treat cardiometabolic disease.

Regulation of glucose and lipid metabolism in health and disease

Glucose and fatty acids are the major sources of energy for human body. Cholesterol, the most abundant sterol in mammals, is a key component of cell membranes although it does not generate ATP. The metabolisms of glucose, fatty acids and cholesterol are often intertwined and regulated. For example, glucose can be converted to fatty acids and cholesterol through de novo lipid biosynthesis pathways. Excessive lipids are secreted in lipoproteins or stored in lipid droplets. The metabolites of glucose and lipids are dynamically transported intercellularly and intracellularly, and then converted to other molecules in specific compartments. The disorders of glucose and lipid metabolism result in severe diseases including cardiovascular disease, diabetes and fatty liver. This review summarizes the major metabolic aspects of glucose and lipid, and their regulations in the context of physiology and diseases.

Advances of Molecular Markers and Their Application for Body Variables and Carcass Traits in Qinchuan Cattle

This review considers the unique characteristics of Chinese cattle and intramuscular fat content (IMF) as factors influencing meat quality, including tenderness, flavor, and juiciness of meat. Due to its nutritional qualities, meat contributes to a healthy and balanced diet. The intramuscular fat content and eating quality of beef are influenced by many factors, which can generally be divided into on-farm and pre-slaughter factors (breed, sex of cattle, age at slaughter, housing system, diet, and pre-slaughter handling) and postmortem factors (post-slaughter processing, chilling temperature, and packaging). Meat quality traits can also be influenced by the individual genetic background of the animal. Worldwide, the function of genes and genetic polymorphisms that have potential effects on fattening of cattle and beef quality have been investigated. The use of DNA markers is recognized as a powerful and efficient approach to achieve genetic gain for desirable phenotypic characteristics, which is helpful for economic growth. The polymorphisms of the SIRT4, SIRT6, SIRT7, CRTC3, ABHD5, KLF6, H-FABP, and ELOVL6 genes for body and growth characteristics of cattle, and also for beef quality, are considered with the aim of highlighting the significance of beef intramuscular fat content, and that growth, body, and meat quality characteristics are polygenically regulated.

Macrophage ABHD5 Suppresses NFκB-Dependent Matrix Metalloproteinase Expression and Cancer Metastasis

Metabolic reprogramming in tumor-associated macrophages (TAM) is associated with cancer development, however, the role of macrophage triglyceride metabolism in cancer metastasis is unclear. Here, we showed that TAMs exhibited heterogeneous expression of abhydrolase domain containing 5 (ABHD5), an activator of triglyceride hydrolysis, with migratory TAMs expressing lower levels of ABHD5 compared with the nonmigratory TAMs. ABHD5 expression in macrophages inhibited cancer cell migration in vitro in xenograft models and in genetic cancer models. The effects of macrophage ABHD5 on cancer cell migration were dissociated from its metabolic function as neither triglycerides nor ABHD5-regulated metabolites from macrophages affected cancer cell migration. Instead, ABHD5 deficiency in migrating macrophages promoted NFκB p65-dependent production of matrix metalloproteinases (MMP). ABHD5 expression negatively correlated with MMP expression in TAMs and was associated with better survival in patients with colorectal cancer. Taken together, our findings show that macrophage ABHD5 suppresses NFκB-dependent MMP production and cancer metastasis and may serve as a prognostic marker in colorectal cancer. SIGNIFICANCE: These findings highlight the mechanism by which reduced expression of the metabolic enzyme ABHD5 in macrophages promotes cancer metastasis.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/21/5513/F1.large.jpg.

Hepatic NPC1L1 overexpression attenuates alcoholic autophagy in mice

Alcohol consumption causes liver steatosis in humans. Metabolic disorders of lipids are one of the factors that cause liver steatosis in hepatocytes. Hepatic Niemann‑Pick C1‑like 1 (NPC1L1) regulates lipid homeostasis in mammals. The relationship between NPC1L1 and autophagy in those with a history of alcohol abuse is unclear. The present study aimed to investigate the function of NPC1L1 in the activation of hepatic autophagy in a mouse model with a human (h)NPC1L1 transgene under alcohol feeding conditions. The mice expressing hNPC1L1 (Ad‑L1) or controls (Ad‑null) were created by retro‑orbital adenovirus injection. The Ad‑L1 and Ad‑null mice were fed with alcohol or a non‑alcoholic diet to mimic chronic alcohol consumption in humans. Hepatic autophagy was demonstrated in isolated primary hepatocytes by monitoring autophagic vacuoles under fluorescence microscopy, and by western blotting for autophagic makers. Isolated hepatocytes from the livers of Ad‑L1 mice were treated with different doses of ezetimibe to study the restoration of autophagy. Chronic alcohol feeding caused liver injury and steatosis, shown by significantly higher levels of plasma alanine transaminase and aspartate transaminase activity, and by hematoxylin and eosin staining in Ad‑L1 and Ad‑null mice. Compared to Ad‑null control mice, the microtubule‑associated proteins 1A/1B light chain 3 (LC3) particles in the isolated hepatocytes of Ad‑L1 mice were decreased, both under alcohol and non‑alcoholic feeding. The ratio of LC3II/LC3I was significantly decreased, and the level of p62/sequestosome‑1 protein was significantly increased in Ad‑L1 mice compared with Ad‑null mice after alcohol feeding. Levels of LC3II protein were statistically increased in hepatocytes isolated from Ad‑L1 mice with ezetimibe treatment. The increase in LC3II expression was dose dependent. Within the tested range, it reached its highest level at 40 µM. The livers of Ad‑L1 mice represent a more human‑like state for the study of hepatic autophagy. Hepatic expression of human NPC1L1 resulted in an inhibition of autophagy; it may contribute to alcoholic fatty liver disease in humans.

The biogenesis of lipid droplets: Lipids take center stage

Lipid droplets (LDs) are multi-functional cellular organelles that store energy, and regulate many aspects of cell physiology. However, our understanding of the biogenesis of LDs remains very limited. Originating from the endoplasmic reticulum (ER), LDs are highly unique organelles in that each LD is bounded by a monolayer of amphipathic lipids. Recent progress has unveiled critical roles of non-bilayer lipids in LD formation. For instance, non-bilayer lipids such as lysophospholipids, diacylglycerol and phosphatidic acid (PA) can impact the curvature, surface and line tension of the ER, thereby impacting LD biogenesis. Two well-known regulators of LD formation, FIT2/FITM2 and seipin, have both been implicated in controlling the metabolism and/or distribution of non-bilayer lipids. We summarize and integrate these recent advances and propose that non-bilayer lipids may play a critical role in each step of LD biogenesis.

HILPDA Regulates Lipid Metabolism, Lipid Droplet Abundance, and Response to Microenvironmental Stress in Solid Tumors

Accumulation of lipid droplets has been observed in an increasing range of tumors. However, the molecular determinants of this phenotype and the impact of the tumor microenvironment on lipid droplet dynamics are not well defined. The hypoxia-inducible and lipid droplet associated protein HILPDA is known to regulate lipid storage and physiologic responses to feeding conditions in mice, and was recently shown to promote hypoxic lipid droplet formation through inhibition of the rate-limiting lipase adipose triglyceride lipase (ATGL). Here, we identify fatty acid loading and nutrient deprivation-induced autophagy as stimuli of HILPDA-dependent lipid droplet growth. Using mouse embryonic fibroblasts and human tumor cells, we found that genetic ablation of HILPDA compromised hypoxia-fatty acid- and starvation-induced lipid droplet formation and triglyceride storage. Nutrient deprivation upregulated HILPDA protein posttranscriptionally by a mechanism requiring autophagic flux and lipid droplet turnover, independent of HIF1 transactivation. Mechanistically, loss of HILPDA led to elevated lipolysis, which could be corrected by inhibition of ATGL. Lipidomic analysis revealed not only quantitative but also qualitative differences in the glycerolipid and phospholipid profile of HILPDA wild-type and knockout cells, indicating additional HILPDA functions affecting lipid metabolism. Deletion studies of HILPDA mutants identified the N-terminal hydrophobic domain as sufficient for targeting to lipid droplets and restoration of triglyceride storage. In vivo, HILPDA-ablated cells showed decreased intratumoral triglyceride levels and impaired xenograft tumor growth associated with elevated levels of apoptosis. IMPLICATIONS: Tumor microenvironmental stresses induce changes in lipid droplet dynamics via HILPDA. Regulation of triglyceride hydrolysis is crucial for cell homeostasis and tumor growth.

Glucagon Receptor Signaling and Glucagon Resistance

Hundred years after the discovery of glucagon, its biology remains enigmatic. Accurate measurement of glucagon has been essential for uncovering its pathological hypersecretion that underlies various metabolic diseases including not only diabetes and liver diseases but also cancers (glucagonomas). The suggested key role of glucagon in the development of diabetes has been termed the bihormonal hypothesis. However, studying tissue-specific knockout of the glucagon receptor has revealed that the physiological role of glucagon may extend beyond blood-glucose regulation. Decades ago, animal and human studies reported an important role of glucagon in amino acid metabolism through ureagenesis. Using modern technologies such as metabolomic profiling, knowledge about the effects of glucagon on amino acid metabolism has been expanded and the mechanisms involved further delineated. Glucagon receptor antagonists have indirectly put focus on glucagon's potential role in lipid metabolism, as individuals treated with these antagonists showed dyslipidemia and increased hepatic fat. One emerging field in glucagon biology now seems to include the concept of hepatic glucagon resistance. Here, we discuss the roles of glucagon in glucose homeostasis, amino acid metabolism, and lipid metabolism and present speculations on the molecular pathways causing and associating with postulated hepatic glucagon resistance.

The α/β-hydrolase domain-containing 4- and 5-related phospholipase Pummelig controls energy storage in Drosophila

Triglycerides (TGs) are the main energy storage form that accommodates changing organismal energy demands. In Drosophila melanogaster, the TG lipase Brummer is centrally important for body fat mobilization. Its gene brummer (bmm) encodes the ortholog of mammalian adipose TG lipase, which becomes activated by α/β-hydrolase domain-containing 5 (ABHD5/CGI-58), one member of the paralogous gene pair, α/β-hydrolase domain-containing 4 (ABHD4) and ABHD5 In Drosophila, the pummelig (puml) gene encodes the single sequence-related protein to mammalian ABHD4/ABHD5 with unknown function. We generated puml deletion mutant flies, that were short-lived as a result of lipid metabolism changes, stored excess body fat at the expense of glycogen, and exhibited ectopic fat storage with altered TG FA profile in the fly kidneys, called Malpighian tubules. TG accumulation in puml mutants was not associated with increased food intake but with elevated lipogenesis; starvation-induced lipid mobilization remained functional. Despite its structural similarity to mammalian ABHD5, Puml did not stimulate TG lipase activity of Bmm in vitro. Rather, Puml acted as a phospholipase that localized on lipid droplets, mitochondria, and peroxisomes. Together, these results show that the ABHD4/5 family member Puml is a versatile phospholipase that regulates Drosophila body fat storage and energy metabolism.

PNPLA3, CGI-58, and Inhibition of Hepatic Triglyceride Hydrolysis in Mice

A variant (148M) in patatin-like phospholipase domain-containing protein 3 (PNPLA3) is a major risk factor for fatty liver disease. Despite its clinical importance, the pathogenic mechanism linking the variant to liver disease remains poorly defined. Previously, we showed that PNPLA3(148M) accumulates to high levels on hepatic lipid droplets (LDs). Here we examined the effect of that accumulation on triglyceride (TG) hydrolysis by adipose triglyceride lipase (ATGL), the major lipase in the liver. As expected, overexpression of ATGL in cultured hepatoma (HuH-7) cells depleted the cells of LDs, but unexpectedly, co-expression of PNPLA3(wild type [WT] or 148M) with ATGL inhibited that depletion. The inhibitory effect of PNPLA3 was not caused by the displacement of ATGL from LDs. We tested the hypothesis that PNPLA3 interferes with ATGL activity by interacting with its cofactor, comparative gene identification-58 (CGI-58). Evidence supporting such an interaction came from two findings. First, co-expression of PNPLA3 and CGI-58 resulted in LD depletion in cultured cells, but expression of PNPLA3 alone did not. Second, PNPLA3 failed to localize to hepatic LDs in liver-specific Cgi-58 knockout (KO) mice. Moreover, overexpression of PNPLA3(148M) increased hepatic TG levels in WT, but not in Cgi-58 KO mice. Thus, the pro-steatotic effects of PNPLA3 required the presence of CGI-58. Co-immunoprecipitation and pulldown experiments in livers of mice and in vitro using purified proteins provided evidence that PNPLA3 and CGI-58 can interact directly. Conclusion: Taken together, these findings are consistent with a model in which PNPLA3(148M) promotes steatosis by CGI-58-dependent inhibition of ATGL on LDs.

A homolog of Arabidopsis SDP1 lipase in Nannochloropsis is involved in degradation of de novo-synthesized triacylglycerols in the endoplasmic reticulum

Organisms of the microalgal genus Nannochloropsis produce high levels of triacylglycerols (TAGs), an efficient raw material for biofuels. A complete understanding of the TAG-breakdown pathway is critical for improving the productivity of TAGs to meet future needs. Among a number of lipases annotated as TAG lipase in the genomes of every organism, Arabidopsis SUGAR-DEPENDENT 1 (AtSDP1) lipases are characterized as a type of crucial TAG lipase in plants, similar to ScTgl3-5 in Saccharomyces cerevisiae. Homologs of the AtSDP1 TAG lipases are universally found in the genomes of plants, fungi, and algae. Here we identified two homologs of AtSDP1 TAG lipases in the oleaginous microalga species Nannochloropsis oceanica, NoTGL1 and NoTGL2. We generated single- and double-knockout strains for these lipases by homologous recombination. Whereas overall TAG content in the NoTGL2 single-knockout mutant was identical to that of wild type, the NoTGL1 knockout showed a two-fold increase in TAG content per cell in early log phase under nutrient-sufficient conditions without affecting growth. Homologs of AtSDP1 in S. cerevisiae are localized to the surface of lipid droplets, and AtSDP1 is transported from peroxisomes to the surface of lipid droplets. In contrast, NoTGL1 localized to the endoplasmic reticulum in both Nannochloropsis and yeast. We suggest that homologs of AtSDP1 lipases in Nannochloropsis modulate de novo TAG biosynthesis in the endoplasmic reticulum, unlike the roles of these lipases in other organisms. These results provide important insights into the mechanisms of TAG metabolism catalyzed by homologs of AtSDP1 lipase, which are highly conserved across species.

Assessment of the Main Compounds of the Lipolytic System in Treadmill Running Rats: Different Response Patterns between the Right and Left Ventricle

The aim of the present study was to investigate the time and intensity dependent effects of exercise on the heart components of the lipolytic complex. Wistar rats ran on a treadmill with the speed of 18 m/min for 30 min (M30) or 120 min (M120) or with the speed of 28 m/min for 30 min (F30). The mRNA and protein expressions of the compounds adipose triglyceride lipase (ATGL), comparative gene identification-58 (CGI-58), G0/G1 switch gene 2 (G0S2), hormone sensitive lipase (HSL) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) were examined by real-time PCR and Western blot, respectively. Lipid content of free fatty acids (FFA), diacylglycerols (DG) and triacylglycerols (TG) were estimated by gas liquid chromatography. We observed virtually no changes in the left ventricle lipid contents and only minor fluctuations in its ATGL mRNA levels. This was in contrast with its right counterpart i.e., the content of TG and DG decreased in response to both increased duration and intensity of a run. This occurred in tandem with increased mRNA expression for ATGL, CGI-58 and decreased expression of G0S2. It is concluded that exercise affects behavior of the components of the lipolytic system and the lipid content in the heart ventricles. However, changes observed in the left ventricle did not mirror those in the right one.

Thyroid involvement in Chanarin-Dorfman syndrome in adults in the largest series of patients carrying the same founder mutation in ABHD5 gene

Background

Chanarin-Dorfman syndrome (CDS) is a rare syndromic disease related to an accumulation of triacylglycerol in most organs. The aim of our study was to investigate various organs in a large series of CDS patients.

Results

We report for the first time thyroid function impairment in CDS. Among 12 investigated patients, 7 showed thyroid function impairment. All of them were over 30 of age. The 5 remaining investigated patients with normal thyroid function were under 30. Thyroid loss of function is an unknown clinical feature of CDS that could gradually develop with age. Thyroid ultrasound showed an abnormal aspect in all investigated patients (6 with thyroid impairment and 3 with normal thyroid function). Cervical MRI done in 2 patients with thyroid impairment showed fat infiltration of thyroid parenchyma. Audiogram carried out in 8 of our patients showed sensorineural hearing impairment in all patients, although only 2 patients suffered from clinical hypoacusia. We also demonstrated that kidney could be a more commonly involved organ than previously reported in the literature. A poorly differentiated kidney parenchyma is a common feature in our series. One patient showed cerebellar atrophy and T2 hypersignal of brain’s white matter in MRI. All patients carried the same founder mutation c.773(− 1)G > A in the ABDH5 gene.

Discussion

Aside from the congenital ichthyosiform erythroderma, the most common symptom of CDS, in addition to other organs involvement frequently reported in the literature, we described thyroid dysfunction, an unreported feature, probably related to the lipid infiltration of the thyroid parenchyma. The association found between age and hypothyroidism in CDS patients could explain the gradually development of thyroid disease with age.

Conclusion

We reported a thyroid dysfunction and unreported ultrasonographic aspects of kidneys and cerebral MRI in CDS patients.

Methods

We performed clinical analyses in 15 patients in whom thyroid, liver, ocular, kidney, skeletal muscle and neurological involvement were explored. Genetic and molecular explorations were performed by direct sequence analysis. Software SPSS, Fisher’s exact test and ANOVA were used for statistical analyses.

Electronic supplementary material

The online version of this article (10.1186/s13023-019-1095-4) contains supplementary material, which is available to authorized users.

Functional diversity of glycerolipid acylhydrolases in plant metabolism and physiology

Most current knowledge about plant lipid metabolism has focused on the biosynthesis of lipids and their transport between different organelles. However, lipid composition changes during development and in response to environmental cues often go beyond adjustments of lipid biosynthesis. When lipids have to be removed to adjust the extent of membranes during down regulation of photosynthesis, or lipid composition has to be adjusted to alter the biophysical properties of membranes, or lipid derived chemical signals have to be produced, lipid-degrading enzymes come into play. This review focuses on glycerolipid acylhydrolases that remove acyl groups from glycerolipids and will highlight their roles in lipid remodeling and lipid-derived signal generation. One emerging theme is that these enzymes are involved in the dynamic movement of acyl groups through different lipid pools, for example from polar membrane lipids to neutral lipids sequestered in lipid droplets during de novo triacylglycerol synthesis. Another example of acyl group sequestration in the form of triacylglycerols in lipid droplets is membrane lipid remodeling in response to abiotic stresses. Fatty acids released for membrane lipids can also give rise to potent signaling molecules and acylhydrolases are therefore often the first step in initiating the formation of these lipid signals.

Dynamic interactions of ABHD5 with PNPLA3 regulate triacylglycerol metabolism in brown adipocytes

Patatin-Like Phospholipase Domain Containing 2 (PNPLA2)/Adipose Triglyceride Lipase (ATGL) and PNPLA3/Adiponutrin are close paralogs that appear to have opposite functions on triacylglycerol (TAG) mobilization and storage. PNPLA2/ATGL is a major triglyceride lipase in adipose tissue and liver, whereas a common human variant of PNPLA3, I148M, greatly increases risk of hepatosteatosis. Nonetheless, the function of PNPLA3 and the mechanism by which the I148M variant promotes TAG accumulation are poorly understood. Here we demonstrate that PNPLA3 strongly interacts with α/β hydrolase domain-containing 5 (ABHD5/CGI-58), an essential co-activator of PNPLA2/ATGL. Molecular imaging experiments demonstrate that PNPLA3 effectively competes with PNPLA2/ATGL for ABHD5, and that PNPLA3 I148M is more effective in this regard. Inducible overexpression of PNPLA3 I148M greatly suppressed PNPLA2/ATGL-dependent lipolysis and triggered massive TAG accumulation in brown adipocytes, and these effects were dependent on ABHD5. The interaction of PNPLA3 and ABHD5 can be regulated by fatty acid supplementation and synthetic ABHD5 ligands, raising the possibility that this interaction might be targeted for treatment of fatty liver disease.

Identification of an intrinsic lysophosphatidic acid acyltransferase activity in the lipolytic inhibitor G0/G1 switch gene 2 (G0S2)

G₀/G₁ switch gene 2 (G0S2) is a specific inhibitor of adipose triglyceride lipase (ATGL), the rate-limiting enzyme for intracellular lipolysis. Recent studies show that G0S2 plays a critical role in promoting triacylglycerol (TG) accumulation in the liver, and its encoding gene is a direct target of a major lipogenic transcription factor liver X receptor (LXR)α. Here we sought to investigate a lipolysis-independent role of G0S2 in hepatic triglyceride synthesis. Knockdown of G0S2 decreased hepatic TG content in mice with ATGL ablation. Conversely, overexpression of G0S2 promoted fatty acid incorporation into TGs and diacylglycerols in both wild-type and ATGL-deficient hepatocytes. Biochemical characterization showed that G0S2 mediates phosphatidic acid synthesis from lysophosphatidic acid (LPA) and acyl-coenzyme A. In response to a high-sucrose lipogenic diet, G0S2 is up-regulated via LXRα and required for the increased TG accumulation in liver. Furthermore, deletion of a distinct 4-aa motif necessary for the LPA-specific acyltransferase (LPAAT) activity impaired G0S2's ability to mediate TG synthesis both in vitro and in vivo. These studies identify G0S2 as a dual-function regulator of lipid metabolism as well as a novel mechanism whereby hepatic TG storage is promoted in response to lipogenic stimulation. In addition to its role as a lipolytic inhibitor, G0S2 is capable of directly promoting TG synthesis by acting as a lipid-synthesizing enzyme.-Zhang, X., Xie, X., Heckmann, B. L., Saarinen, A. M., Gu, H., Zechner, R., Liu, J. Identification of an intrinsic lysophosphatidic acid acyltransferase activity in the lipolytic inhibitor G₀/G₁ switch gene 2 (G0S2).

Genetically modified mouse models to study hepatic neutral lipid mobilization

Excessive accumulation of triacylglycerol is the common denominator of a wide range of clinical pathologies of liver diseases, termed non-alcoholic fatty liver disease. Such excessive triacylglycerol deposition in the liver is also referred to as hepatic steatosis. Although liver steatosis often resolves over time, it eventually progresses to steatohepatitis, liver fibrosis and cirrhosis, with associated complications, including liver failure, hepatocellular carcinoma and ultimately death of affected individuals. From the disease etiology it is obvious that a tight regulation between lipid uptake, triacylglycerol synthesis, hydrolysis, secretion and fatty acid oxidation is required to prevent triacylglycerol deposition in the liver. In addition to triacylglycerol, also a tight control of other neutral lipid ester classes, i.e. cholesteryl esters and retinyl esters, is crucial for the maintenance of a healthy liver. Excessive cholesteryl ester accumulation is a hallmark of cholesteryl ester storage disease or Wolman disease, which is associated with premature death. The loss of hepatic vitamin A stores (retinyl ester stores of hepatic stellate cells) is incidental to the onset of liver fibrosis. Importantly, this more advanced stage of liver disease usually does not resolve but progresses to life threatening stages, i.e. liver cirrhosis and cancer. Therefore, understanding the enzymes and pathways that mobilize hepatic neutral lipid esters is crucial for the development of strategies and therapies to ameliorate pathophysiological conditions associated with derangements of hepatic neutral lipid ester stores, including liver steatosis, steatohepatitis, and fibrosis. This review highlights the physiological roles of enzymes governing the mobilization of neutral lipid esters at different sites in liver cells, including cytosolic lipid droplets, endoplasmic reticulum, and lysosomes. This article is part of a Special Issue entitled Molecular Basis of Disease: Animal models in liver disease.

Molecular Mechanisms in Skeletal Muscle Underlying Insulin Resistance in Women Who Are Lean With Polycystic Ovary Syndrome

CONTEXT

Skeletal muscle molecular mechanisms underlying insulin resistance in women with polycystic ovary syndrome (PCOS) are poorly understood.

OBJECTIVE

To provide insight into mechanisms regulating skeletal muscle insulin resistance in women who are lean with PCOS.

PARTICIPANTS AND METHODS

A hyperinsulinemic-euglycemic clamp with skeletal muscle biopsies was performed. Thirteen women who are lean who have hyperandrogenism and PCOS and seven age- and body mass index-matched healthy control subjects were enrolled. Skeletal muscle protein expression and phosphorylation were analyzed by Western blotting and intramuscular lipid content was measured by thin-layer chromatography.

RESULTS

Women with PCOS had 25% lower whole-body insulin sensitivity and 40% lower plasma adiponectin concentration than in control subjects. Intramuscular triacylglycerol, sn-1.3 diacylglycerol, and ceramide contents in skeletal muscle were higher (40%, 50%, and 300%, respectively) in women with PCOS than in control subjects. Activation of insulin signaling did not differ between groups. In women with PCOS, the insulin-stimulated glucose oxidation was reduced and insulin-stimulated dephosphorylation of pyruvate dehydrogenase (PDH) Ser293 was absent. AMP-activated protein kinase (AMPK) α2 protein expression and basal Thr172 phosphorylation were 45% and 50% lower in women with PCOS than in control subjects, respectively.

CONCLUSIONS

Whole-body insulin resistance in women who are lean who have hyperandrogenism and PCOS was not related to changes in the proximal part of the insulin signaling cascade in skeletal muscle despite lipid accumulation. Rather, reduced insulin sensitivity was potentially related to plasma adiponectin levels playing a modulating role in human skeletal muscle via AMPK. Furthermore, abnormal PDH regulation may contribute to reduced whole-body metabolic flexibility and thereby insulin resistance.

Glucagon Receptor Signaling and Lipid Metabolism

Glucagon is secreted from the pancreatic alpha cells upon hypoglycemia and stimulates hepatic glucose production. Type 2 diabetes is associated with dysregulated glucagon secretion, and increased glucagon concentrations contribute to the diabetic hyperglycemia. Antagonists of the glucagon receptor have been considered as glucose-lowering therapy in type 2 diabetes patients, but their clinical applicability has been questioned because of reports of therapy-induced increments in liver fat content and increased plasma concentrations of low-density lipoprotein. Conversely, in animal models, increased glucagon receptor signaling has been linked to improved lipid metabolism. Glucagon acts primarily on the liver and by regulating hepatic lipid metabolism glucagon may reduce hepatic lipid accumulation and decrease hepatic lipid secretion. Regarding whole-body lipid metabolism, it is controversial to what extent glucagon influences lipolysis in adipose tissue, particularly in humans. Glucagon receptor agonists combined with glucagon-like peptide 1 receptor agonists (dual agonists) improve dyslipidemia and reduce hepatic steatosis. Collectively, emerging data support an essential role of glucagon for lipid metabolism.

The role of polyamines in the regulation of macrophage polarization and function

Naturally occurring polyamines are ubiquitously distributed and play important roles in cell development, amino acid and protein synthesis, oxidative DNA damage, proliferation, and cellular differentiation. Macrophages are essential in the innate immune response, and contribute to tissue remodeling. Naïve macrophages have two major potential fates: polarization to (1) the classical pro-inflammatory M1 defense response to bacterial pathogens and tumor cells, and (2) the alternatively activated M2 response, induced in the presence of parasites and wounding, and also implicated in the development of tumor-associated macrophages. ODC, the rate-limiting enzyme in polyamine synthesis, leads to an increase in putrescine levels, which impairs M1 gene transcription. Additionally, spermidine and spermine can regulate translation of pro-inflammatory mediators in activated macrophages. In this review, we focus on polyamines in macrophage activation patterns in the context of gastrointestinal inflammation and carcinogenesis. We seek to clarify mechanisms of innate immune regulation by polyamine metabolism and potential novel therapeutic targets.

Metabolic lipid muscle disorders: biomarkers and treatment

Lipid storage myopathies (LSMs) are metabolic disorders of the utilization of fat in muscles due to several different defects. In this review, a molecular update of LSMs is presented and recent attempts of finding treatment options are discussed. The main topics discussed are: primary carnitine deficiency, riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency, neutral lipid storage disorders and carnitine palmitoyl transferase deficiency. The most frequent presentations and genetic abnormalities are summarized. We present their diagnosis utilizing biomedical and morphological biomarkers and possible therapeutic interventions. The treatment of these metabolic disorders is a subject of active translational research but appears, in some cases, still elusive.

Central injection of oxytocin reduces food intake and affects hypothalamic and adipose tissue gene expression in chickens

Oxytocin (OT) is a well-characterized neurotransmitter that participates in a wide range of physiological processes including the inhibition of food intake. The avian ortholog, mesotocin (MT), differs from OT by a single amino acid. Little is known regarding the function of OT in regulating energy balance in birds; thus, this study was designed to determine the effects of central OT injection on food intake and adipose tissue physiology in chicks. At 4-d post-hatch, broiler chicks were fasted for 3 h and injected intracerebroventricularly with 0 (vehicle), 0.63, 2.5, 5.0, or 10 nmol OT. Oxytocin decreased food and water intake during the entire 180-min observation period. The reduction in water intake was likely not prandial because chicks that were food restricted after OT injection also drank less. There was increased c-Fos immunoreactivity in several appetite-associated hypothalamic nuclei in OT-injected chicks at 1 h, including the arcuate (ARC), dorsomedial nucleus (DMN), lateral hypothalamus (LH), paraventricular nucleus (PVN), and ventromedial hypothalamus (VMH). OT treatment was associated with reduced hypothalamic corticotropin-releasing factor (CRF) mRNA and increased cloacal temperature at 1 h post-injection. We then investigated appetite- and adipose tissue-associated effects of OT in chicks from lines that have undergone long-term selection for either low (LWS) or high (HWS) juvenile body weight. Central injection of OT decreased food intake in both lines with the magnitude of response greater in the HWS than LWS chicks. Adipose tissue abundance of fatty acid-binding protein 4, monoglyceride lipase (MGLL), MT, and perilipin-1 mRNA was greater in LWS than HWS chicks. Lipoprotein lipase, MGLL, and MT mRNAs increased in response to OT injection in LWS but not HWS chicks. In conclusion, central injection of OT induced anorexia, reduced water intake, increased body temperature, and was associated with activation of the ARC, DMN, LH, PVN, and VMH in the hypothalamus. The effects on appetite and body temperature may involve CRF signaling in the hypothalamus and lipolysis in the adipose tissue, respectively. There were differences in the appetite, and adipose tissue response to OT in body weight-selected lines of chicks supports that MT plays a role in energy balance regulation in chickens.

Oncogenic role of ABHD5 in endometrial cancer

Background

Abhydrolase domain containing 5 (ABHD5) functions as a tumor suppressor in colorectal and prostate cancers. The aim of this study was to investigate the roles of ABHD5 in endometrial cancer.

Materials and methods

ABHD5 expression was detected in clinical samples by immunohistochemical staining. Cell proliferation and invasion were evaluated with the Cell Counting Kit-8 and Transwell assay, respectively. Western blotting was performed to analyze protein expression. Glucose uptake was assessed by 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose. Lactate production was detected by a lactate assay kit.

Results

In the present study, ABHD5 was overexpressed in endometrial cancer tissues, and its expression was closely correlated with the International Federation of Gynecology and Obstetrics (FIGO) stage and lymph node metastasis. In addition, we observed that the knockdown of ABHD5 inhibited cell proliferation, invasion, glucose uptake and lactate production in HEC-1A cells, which expressed high levels of ABHD5. Conversely, the opposite effects were observed when ABHD5 was ectopically expressed in Ishikawa cells, which had low levels of ABHD5. Furthermore, the changes in glycolysis regulators (enolase 1 [ENO1], glucose transporter 1 [GLUT1] and lactate dehydrogenase A [LDHA]) and epithelial-to-mesenchymal transition-related proteins (E-cadherin and Snail) in HEC-1A cells with ABHD5 knockdown were consistent with the effects of ABHD5 on glycolysis and cell invasion. Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) was increased, while the phosphorylated AKT (p-AKT) was decreased when ABHD5 was downregulated. Notably, treatment with the allosteric AKT inhibitor MK-2206 completely abolished the effects caused by ABHD5 overexpression in Ishikawa cells. Finally, ABHD5 knockdown potently suppressed tumor growth in vivo.

Conclusion

Overall, these results suggest that ABHD5 may play an oncogenic role in endometrial cancer via the AKT pathway.

Sequence analysis and structure prediction of ABHD16A and the roles of the ABHD family members in human disease

Abhydrolase domain containing 16A (ABHD16A) is a member of the α/β hydrolase domain-containing (ABHD) protein family and is expressed in a variety of animal cells. Studies have shown that ABHD16A has acylglycerol lipase and phosphatidylserine lipase activities. Its gene location in the main histocompatibility complex (MHC) III gene cluster suggests that this protein may participate in the immunomodulation of the body. The results of studies investigating nearly 20 species of ABHDs reveal that the ABHD proteins are key factors in metabolic regulation and disease occurrence and development. In this paper, we summarize the related progress regarding the function of ABHD16A and other ABHD proteins. A prediction of the active sites and structural domains of ABHD16A and an analysis of the amino acid sites are included. Moreover, we analysed the amino acid sequences of the ABHD16A molecules in different species and provide an overview of the related functions and diseases associated with these proteins. The functions and diseases related to ABHD are systematically summarized and highlighted. Future research directions for studies investigating the functions and mechanisms of these proteins are also suggested. Further studies investigating the function of ABHD proteins may further confirm their positions as important determinants of lipid metabolism and related diseases.

HCV Pit Stop at the Lipid Droplet: Refuel Lipids and Put on a Lipoprotein Coat before Exit

The replication cycle of the liver-tropic hepatitis C virus (HCV) is tightly connected to the host lipid metabolism, during the virus entry, replication, assembly and egress stages, but also while the virus circulates in the bloodstream. This interplay coins viral particle properties, governs viral cell tropism, and facilitates immune evasion. This review summarizes our knowledge of these interactions focusing on the late steps of the virus replication cycle. It builds on our understanding of the cell biology of lipid droplets and the biosynthesis of liver lipoproteins and attempts to explain how HCV hijacks these organelles and pathways to assemble its lipo-viro-particles. In particular, this review describes (i) the mechanisms of viral protein translocation to and from the lipid droplet surface and the orchestration of an interface between replication and assembly complexes, (ii) the importance of the triglyceride mobilization from the lipid droplets for HCV assembly, (iii) the interplay between HCV and the lipoprotein synthesis pathway including the role played by apolipoproteins in virion assembly, and finally (iv) the consequences of these complex virus–host interactions on the virion composition and its biophysical properties. The wealth of data accumulated in the past years on the role of the lipid metabolism in HCV assembly and its imprint on the virion properties will guide vaccine design efforts and reinforce our understanding of the hepatic lipid metabolism in health and disease.

n-3 polyunsaturated fatty acids provoke a specific transcriptional profile in rabbit adipose-derived stem cells in vitro

Adipose-derived stem cells (ADSCs) possess multipotent properties, and their proper functionality is essential for further development of metabolic disorders. In the current study, we explored the impact of two n-3 LC-PUFAs (long-chain polyunsaturated fatty acids, DHA-docosahexaenoic; C22:6, and EPA-eicosapentaenoic; C20:5) on a specific profile of lipolytic-related gene expressions in the in vitro-differentiated subcutaneous and visceral ADSCs from rabbits. The subcutaneous and visceral ADSCs were obtained from 28-day-old New Zealand rabbits. The primary cells were cultured up to passage 4 and were induced for adipogenic differentiation. Thereafter, the differentiated cells were treated with 100 µg EPA or DHA for 48 hr. The total mRNA was isolated and target genes expression evaluated by real-time RCR. The results demonstrated that treatment of rabbit ADSCs with n-3 PUFAs significantly enhanced mRNA expression of Perilipin A, while the upregulation of leptin and Rab18 genes was seen mainly in ADSCs from visceral adipose tissue. Moreover, the EPA significantly enhanced PEDF (Pigment Derived Epithelium Factor) mRNA expression only in visceral cells. Collectively, the results suggest activation of an additional lipolysis pathway most evident in visceral cells. The data obtained in our study indicate that in vitro EPA up-regulates the mRNA expression of the studied lipolysis-associated genes stronger than DHA mainly in visceral rabbit ADSCs.

Metabolic engineering for enhanced oil in biomass

The world is hungry for energy. Plant oils in the form of triacylglycerol (TAG) are one of the most reduced storage forms of carbon found in nature and hence represent an excellent source of energy. The myriad of applications for plant oils range across foods, feeds, biofuels, and chemical feedstocks as a unique substitute for petroleum derivatives. Traditionally, plant oils are sourced either from oilseeds or tissues surrounding the seed (mesocarp). Most vegetative tissues, such as leaves and stems, however, accumulate relatively low levels of TAG. Since non-seed tissues constitute the majority of the plant biomass, metabolic engineering to improve their low-intrinsic TAG-biosynthetic capacity has recently attracted significant attention as a novel, sustainable and potentially high-yielding oil production platform. While initial attempts predominantly targeted single genes, recent combinatorial metabolic engineering strategies have focused on the simultaneous optimization of oil synthesis, packaging and degradation pathways (i.e., 'push, pull, package and protect'). This holistic approach has resulted in dramatic, seed-like TAG levels in vegetative tissues. With the first proof of concept hurdle addressed, new challenges and opportunities emerge, including engineering fatty acid profile, translation into agronomic crops, extraction, and downstream processing to deliver accessible and sustainable bioenergy.

Neutral Lipid Storage Diseases as Cellular Model to Study Lipid Droplet Function

Neutral lipid storage disease with myopathy (NLSDM) and with ichthyosis (NLSDI) are rare autosomal recessive disorders caused by mutations in the PNPLA2 and in the ABHD5/CGI58 genes, respectively. These genes encode the adipose triglyceride lipase (ATGL) and α-β hydrolase domain 5 (ABHD5) proteins, which play key roles in the function of lipid droplets (LDs). LDs, the main cellular storage sites of triacylglycerols and sterol esters, are highly dynamic organelles. Indeed, LDs are critical for both lipid metabolism and energy homeostasis. Partial or total PNPLA2 or ABHD5/CGI58 knockdown is characteristic of the cells of NLSD patients; thus, these cells are natural models with which one can unravel LD function. In this review we firstly summarize genetic and clinical data collected from NLSD patients, focusing particularly on muscle, skin, heart, and liver damage due to impaired LD function. Then, we discuss how NLSD cells were used to investigate and expand the current structural and functional knowledge of LDs.

Higher lipid turnover and oxidation in cultured human myotubes from athletic versus sedentary young male subjects

In this study we compared fatty acid (FA) metabolism in myotubes established from athletic and sedentary young subjects. Six healthy sedentary (maximal oxygen uptake (VO_2max) ≤ 46 ml/kg/min) and six healthy athletic (VO_2max > 60 ml/kg/min) young men were included. Myoblasts were cultured and differentiated to myotubes from satellite cells isolated from biopsy of musculus vastus lateralis. FA metabolism was studied in myotubes using [¹⁴C]oleic acid. Lipid distribution was assessed by thin layer chromatography, and FA accumulation, lipolysis and re-esterification were measured by scintillation proximity assay. Gene and protein expressions were studied. Myotubes from athletic subjects showed lower FA accumulation, lower incorporation of FA into total lipids, triacylglycerol (TAG), diacylglycerol and cholesteryl ester, higher TAG-related lipolysis and re-esterification, and higher complete oxidation and incomplete β-oxidation of FA compared to myotubes from sedentary subjects. mRNA expression of the mitochondrial electron transport chain complex III gene UQCRB was higher in cells from athletic compared to sedentary. Myotubes established from athletic subjects have higher lipid turnover and oxidation compared to myotubes from sedentary subjects. Our findings suggest that cultured myotubes retain some of the phenotypic traits of their donors.