Defective adipose lipolysis and altered global energy metabolism in mice with adipose overexpression of the lipolytic inhibitor G0/G1 switch gene 2 (G0S2)

Exercise-induced anti-obesity effects in male mice generated by a FOXO1-KLF10 reinforcing loop promoting adipose lipolysis

Exercise combats obesity and metabolic disorders, but the underlying mechanism is incompletely understood. KLF10, a transcription factor involved in various biological processes, has an undefined role in adipose tissue and obesity. Here, we show that exercise facilitates adipocyte-derived KLF10 expression via SIRT1/FOXO1 pathway. Adipocyte-specific knockout of KLF10 blunts exercise-promoted white adipose browning, energy expenditure, fat loss, glucose tolerance in diet-induced obese male mice. Conversely, adipocyte-specific transgenic expression of KLF10 in male mice enhanced the above metabolic profits induced by exercise. Mechanistically, KLF10 interacts with FOXO1 and facilitates the recruitment of KDM4A to form a ternary complex on the promoter regions of Pnpla2 and Lipe genes to promote these key lipolytic genes expression by demethylating H3K9me3 on their promoters, which facilitates lipolysis to defend against obesity in male mice. As a downstream effector responding to exercise, adipose KLF10 could act as a potential target in the fight against obesity.

Interplay of FXN expression and lipolysis in white adipocytes plays a critical role in insulin sensitivity in Friedreich's ataxia mouse model

Frataxin (FXN) is required for iron-sulfur cluster biogenesis, and its loss causes the early-onset neurodegenerative disease Friedreich ataxia (FRDA). Loss of FXN is a susceptibility factor in the development of diabetes, a common metabolic complication after myocardial hypertrophy in patients with FRDA. The underlying mechanism of FXN deficient-induced hyperglycemia in FRDA is, however, poorly understood. In this study, we confirmed that the FXN deficiency mouse model YG8R develops insulin resistance in elder individuals by disturbing lipid metabolic homeostasis in adipose tissues. Evaluation of lipolysis, lipogenesis, and fatty acid β-oxidation showed that lipolysis is most severely affected in white adipose tissues. Consistently, FXN deficiency significantly decreased expression of lipolytic genes encoding adipose triglyceride lipase (Atgl) and hormone-sensitive lipase (Hsl) resulting in adipocyte enlargement and inflammation. Lipolysis induction by fasting or cold exposure remarkably upregulated FXN expression, though FXN deficiency lessened the competency of lipolysis compared with the control or wild type mice. Moreover, we found that the impairment of lipolysis was present at a young age, a few months earlier than hyperglycemia and insulin resistance. Forskolin, an activator of lipolysis, or pioglitazone, an agonist of PPARγ, improved insulin sensitivity in FXN-deficient adipocytes or mice. We uncovered the interplay between FXN expression and lipolysis and found that impairment of lipolysis, particularly the white adipocytes, is an early event, likely, as a primary cause for insulin resistance in FRDA patients at later age.

Artesunate improves glucose and lipid metabolism in db/db mice by regulating the metabolic profile and the MAPK/PI3K/Akt signalling pathway

BACKGROUND

Diabetes is a metabolic disorder characterized by chronic hyperglycaemia. Chronic metabolic abnormalities and long-term hyperglycaemia may result in a wide range of acute and chronic consequences. Previous studies have demonstrated that artesunate(ART) has antidiabetic, anti-inflammatory, antiatherosclerotic, and other beneficial effects, but the specific regulatory mechanism is not completely clear.

AIM

This study investigated the effects of ART on metabolic disorders in type 2 diabetes mellitus (T2DM) model db/db mice and explored the underlying mechanisms involved.

METHODS

C57BL/KsJ-db/db mice were used to identify the targets and molecular mechanism of ART. Metabolomic methods were used to evaluate the efficacy of ART in improving T2DM-related metabolic disorders. Network pharmacology and transcriptomic sequencing were used to analyse the targets and pathways of ART in T2DM. Finally, molecular biology experiments were performed to verify the key targets and pathways selected by network pharmacology and transcriptomic analyses.

RESULTS

After a 7-week ART intervention (160 mg/kg), the glucose and lipid metabolism levels of the db/db mice improved. Additionally, the oxidative stress indices, namely, the MDA and SOD levels, significantly improved (p<0.01). Linoleic acid and glycerophospholipid metabolism, amino acid metabolism, bile acid synthesis, and purine metabolism disorders in db/db mice were partially corrected after ART treatment. Network pharmacology analysis identified important targets of ART for the treatment of metabolic disorders in T2DM . These targets are involved in key signalling pathways, including the highest scores observed for the PI3K/Akt signalling pathway. Transcriptomic analysis revealed that ART could activate the MAPK signalling pathway and two key gene targets, HGK and GADD45. Immunoblotting revealed that ART increases p-PI3K, p-AKT, Glut2, and IRS1 protein expression and suppresses the phosphorylation of p38, ERK1/2, and JNK, returning HGK and GADD45 to their preartesunate levels.

CONCLUSION

Treatment of db/db mice with 160 mg/kg ART for 7 weeks significantly reduced fasting blood glucose and lipid levels. It also improved metabolic imbalances in amino acids, lipids, purines, and bile acids, thereby improving metabolic disorders. These effects are achieved by activating the PI3K/AKT pathway and inhibiting the MAPK pathway, thus demonstrating the efficacy of the drug.

Lipid Storage, Lipolysis, and Lipotoxicity in Obesity

The ratio of free fatty acid (FFA) turnover decreases significantly with the expansion of white adipose tissue. Adipose tissue and dietary saturated fatty acid levels significantly correlate with an increase in fat cell size and number. The G0/G1 switch gene 2 increases lipid content in adipocytes and promotes adipocyte hypertrophy through the restriction of triglyceride (triacylglycerol: TAG) turnover. Hypoxia in obese adipose tissue due to hypertrophic adipocytes results in excess deposition of extracellular matrix (ECM) components. Cluster of differentiation (CD) 44, as the main receptor of the extracellular matrix component regulates cell-cell and cell-matrix interactions including diet-induced insulin resistance. Excess TAGs, sterols, and sterol esters are surrounded by the phospholipid monolayer surface and form lipid droplets (LDs). Once LDs are formed, they grow up because of the excessive amount of intracellular FFA stored and reach a final size. The ratio of FFA turnover/lipolysis decreases significantly with increases in the degree of obesity. Dysfunctional adipose tissue is unable to expand further to store excess dietary lipids, increased fluxes of plasma FFAs lead to ectopic fatty acid deposition and lipotoxicity. Reduced neo-adipogenesis and dysfunctional lipid-overloaded adipocytes are hallmarks of hypertrophic obesity linked to insulin resistance. Obesity-associated adipocyte death exhibits feature of necrosis-like programmed cell death. Adipocyte death is a prerequisite for the transition from hypertrophic to hyperplastic obesity. Increased adipocyte number in obesity has life-long effects on white adipose tissue mass. The positive correlation between the adipose tissue volume and magnetic resonance imaging proton density fat fraction estimation is used for characterization of the obesity phenotype, as well as the risk stratification and selection of appropriate treatment strategies. In obese patients with type 2 diabetes, visceral adipocytes exposed to chronic/intermittent hyperglycemia develop a new microRNAs' (miRNAs') expression pattern. Visceral preadipocytes memorize the effect of hyperglycemia via changes in miRNAs' expression profile and contribute to the progression of diabetic phenotype. Nonsteroidal anti-inflammatory drugs, metformin, and statins can be beneficial in treating the local or systemic consequences of white adipose tissue inflammation. Rapamycin inhibits leptin-induced LD formation. Collectively, in this chapter, the concept of adipose tissue remodeling in response to adipocyte death or adipogenesis, and the complexity of LD interactions with the other cellular organelles are reviewed. Furthermore, clinical perspective of fat cell turnover in obesity is also debated.

Acidosis-induced regulation of adipocyte G0S2 promotes crosstalk between adipocytes and breast cancer cells as well as tumor progression

Bidirectional interactions between cancer cells and their microenvironment govern tumor progression. Among the stromal cells in this microenvironment, adipocytes have been reported to upregulate cancer cell migration and invasion by producing fatty acids. Conversely, cancer cells alter adipocyte phenotype notably via increased lipolysis. We aimed to identify the mechanisms through which cancer cells trigger adipocyte lipolysis and evaluate the functional consequences on cancer progression. Here, we show that cancer cell-induced acidification of the extracellular medium strongly promotes preadipocyte lipolysis through a mechanism that does not involve lipophagy but requires adipose triglyceride lipase (ATGL) activity. This increased lipolysis is triggered mainly by attenuation of the G0/G1 switch gene 2 (G0S2)-induced inhibition of ATGL. G0S2-mediated regulation in preadipocytes affects their communication with breast cancer cells, modifying the phenotype of the cancer cells and increasing their resistance to chemotherapeutic agents in vitro. Furthermore, we demonstrate that the adipocyte-specific overexpression of G0S2 impairs mammary tumor growth and lung metastasis formation in vivo. Our results highlight the importance of acidosis in cancer cell-adipocyte crosstalk and identify G0S2 as the main regulator of cancer-induced lipolysis, regulating tumor establishment and spreading.

Measuring the Rate of Lipolysis in Ex vivo Murine Adipose Tissue and Primary Preadipocytes Differentiated In Vitro

Adipocytes store energy in the form of triglycerides in lipid droplets. This energy can be mobilized via lipolysis, where the fatty acid side chains are sequentially cleaved from the glycerol backbone, resulting in the release of free fatty acids and glycerol. Due to the low expression of glycerol kinase in white adipocytes, glycerol re-uptake rates are negligible, while fatty acid re-uptake is dictated by the fatty acid binding capacity of media components such as albumin. Both glycerol and fatty acid release into media can be quantified by colorimetric assays to determine the lipolytic rate. By measuring these factors at multiple time points, one can determine the linear rate of lipolysis with high confidence. Here, we provide a detailed protocol for the measurement of lipolysis in in vitro differentiated adipocytes and ex vivo adipose tissue from mice. This protocol may also be optimized for other preadipocyte cell lines or adipose tissue from other organisms; considerations and optimization parameters are discussed. This protocol is designed to be useful in determining and comparing the rate of adipocyte lipolysis between mouse models and treatments.

BAP31 depletion inhibited adipogenesis, repressed lipolysis and promoted lipid droplets abnormal growth via attenuating Perilipin1 proteasomal degradation

BAP31 expression was robustly decreased in obese white adipose tissue (WAT). To investigate the roles of BAP31 in lipid metabolism, adipocyte-specific conditional knockout mice (BAP31-ASKO) were generated. BAP31-ASKO mice grow normally as controls, but exhibited reduced lipid accumulation in WAT. Histomorphometric analysis reported increased adipocyte size in BAP31-ASKO mice. Mouse embryonic fibroblasts (MEFs) were induced to differentiation to adipocytes, showed reduced induction of adipogenic markers and attenuated adipogenesis in BAP31-deficient MEFs. BAP31-deficiency inhibited fasting-induced PKA signaling activation and the fasting response. β3-adrenergic receptor agonist-induced lipolysis also was reduced, accompanied by reduced free-fatty acids and glycerol release, and impaired agonist-induced lipolysis from primary adipocytes and adipose explants. BAP31 interacts with Perilipin1 via C-terminal cytoplasmic portion on lipid droplets (LDs) surface. Depletion of BAP31 repressed Perilipin1 proteasomal degradation, enhanced Perilipin1 expression and blocked LDs degradation, which promoted LDs abnormal growth and supersized LDs formation, resulted in adipocyte expansion, thus impaired insulin signaling and aggravated pro-inflammation in WAT. BAP31-deficiency increased phosphatidylcholine/phosphatidylethanolamine ratio, long chain triglycerides and most phospholipids contents. Overall, BAP31-deficiency inhibited adipogenesis and lipid accumulation in WAT, decreased LDs degradation and promoted LDs abnormal growth, pointing the critical roles in modulating LDs dynamics and homeostasis via proteasomal degradation system in adipocytes.

Identification of motifs and mechanisms for lipid droplet targeting of the lipolytic inhibitors G0S2 and HIG2

G0S2 and HIG2 are two selective inhibitors of ATGL (also known as PNPLA2), the key enzyme for intracellular lipolysis. Whereas G0S2 regulates triglyceride (TG) mobilization in adipocytes and hepatocytes, HIG2 functions to enhance intracellular TG accumulation under hypoxic conditions. A homologous hydrophobic domain (HD) is shared by G0S2 and HIG2 (also known as HILPDA) for binding to ATGL. However, the determinants of their lipid droplet (LD) localization are unknown. Here, we study how G0S2 and HIG2 are targeted to LDs, and identify both ATGL-independent and -dependent mechanisms. Structural prediction and studies in cells reveal that ATGL-independent localization of G0S2 to both the endoplasmic reticulum (ER) and LDs is mediated by a hairpin structure consisting of two hydrophobic sequences. Positively charged residues in the hinge region play a crucial role in sorting G0S2, which initially localizes to ER, to LDs. Interestingly, the role of these positive charges becomes dispensable when ATGL is co-expressed. In comparison, HIG2, which lacks a similar hairpin structure, is dependent on ATGL for its full LD targeting. Thus, our studies identify specific structural features and mechanisms for mediating accumulation of these two ATGL inhibitors on LDs.

Middle-Aged Lpaatδ-Deficient Mice Have Altered Metabolic Measures

Lysophosphatidic acid acyltransferases/acylglycerophosphate acyltransferases (LPAATs/AGPATs) are a group of homologous enzymes that catalyze the formation of phosphatidic acid (PA) from lysophosphatidic acid. We have previously reported that LPAATδ/AGPAT4 localizes to mitochondria, suggesting a potential role in energy metabolism. However, in prior studies of young Lpaatδ-deficient mice (age 9–12 weeks old), we found no differences in body weights, food intakes, activity levels, respiratory gas exchange, or energy expenditure compared to their wildtype (Wt) littermates. To test whether Lpaatδ−/− mice may develop differences in metabolic measures with advancing age, we recorded body weights and food intakes, and used metabolic chambers to assess ambulatory and locomotor activity levels, oxygen consumption (VO2), carbon dioxide production (VCO2), respiratory exchange ratio (RER), and total energy expenditure (heat). Fourteen-month-old Lpaatδ−/− mice had significantly lower mean body weights compared to Wt littermate controls (44.6 ± 1.08 g vs. 53.5 ± 0.42 g, respectively), but no significant differences in food intake or activity levels. This phenotypic difference was accompanied by significantly elevated 24 h daily, and 12 h light and dark photoperiod average VO2 (~20% higher) and VCO2 (~30% higher) measures, as well as higher RER and total energy expenditure (heat) values compared to Wt control littermates. Thus, an age-related metabolic phenotype is evident in Lpaatδ−/− mice. Future studies should examine the role of the lipid-modifying enzyme LPAATδ across the lifespan for greater insight into its role in normal and pathophysiology.

Insulin prevents fatty acid induced increase of adipocyte size

Metabolic disorders related to obesity are largely dependent on adipose tissue hypertrophy, which involves adipocyte hypertrophy and increased adipogenesis. Adiposize is regulated by lipid accumulation as a result of increased lipogenesis (mainly lipid uptake in mature adipocytes) and reduced lipolysis. Using realtime 2D cell culture analyses of lipid uptake, we show (1) that high glucose concentration (4.5 g/L) was required to accumulate oleic acid increasing lipid droplet size until unilocularization similar to mature adipocytes in few days, (2) oleic acid reduced Peroxisome-Proliferator Activated Receptor Gamma (PPARG) gene transcription and (3) insulin counteracted oleic acid-induced increase of lipid droplet size. Although the lipolytic activity observed in high versus low glucose (1 g/L) conditions was not altered, insulin was found to inhibit oleic acid induced gene transcription required for lipid storage such as Cell Death Inducing DFFA Like Effectors (CIDEC) and G0S2 (G0 switch gene S2), possibly through PPARA activity. Although this signalling pathway requires more detailed investigation, the results point out the differential mechanisms involved in the pro-adipogenic effect of insulin in absence versus its protective effect on adiposity in presence of oleic acid uptake.

Abbreviations: AICAR, 5-Aminoimidazole-4-carboxamide-1-D-ribofuranoside; AMPK, AMP-Activated protein kinase, ASCs, adipose stem cell; ATGL, adipose triglyceride lipase; BSA, Bovine serum albumin; CEBPA, CCAAT enhancer binding protein alpha; CIDEs, Cell Death Inducing DFFA Like Effectors; dA, differentiated adipocyte; DMEM, Dulbecco’s Modified Eagle’s Medium; FABPs, Fatty Acid Binding Proteins; FAT/CD36, Fatty acid translocase; FCS, Foetal calf serum; FN1, fibronectin 1; FFA, free fatty acid; G0S2, G0 switch gene S2; GLUTs, Glucose transporters; GPR120, G protein-coupled receptor 120; HG, high glucose; HSL, hormone sensitive lipase; INSR, insulin receptor; LG, low glucose; OA, oleic acid; PBS, Phosphate buffer saline; PPARs, Peroxisome-Proliferator Activated Receptors; PKA, Protein kinase cyclic AMP-dependent; PKG, Protein kinase cyclic GMP dependent; PTGS2, cytochrome oxidase 2; RTCA, realtime cell analysis; TG, triglyceride.

Residues of the minimal sequence of G0S2 collectively contribute to ATGL inhibition while C-and N-terminal extensions promote binding to ATGL

The protein encoded by the G0/G1 switch gene 2 (G0S2) is a potent inhibitor of adipose triglyceride lipase (ATGL) and thus an important regulator of intracellular lipolysis. Since dysfunction of lipolysis is associated with metabolic diseases including diabetes and obesity, inhibition of ATGL is considered a therapeutic strategy. G0S2 interacts with ATGL's patatin-domain to mediate non-competitive inhibition, however atomic details of the inhibition mechanism are incompletely understood. Sequences of G0S2 from higher organisms show a highly conserved N-terminal part, including a hydrophobic region covering amino acids 27 to 42. We show that predicted G0S2 orthologs from platypus, chicken and Japanese rice-fish are able to inhibit human and mouse ATGL, emphasizing the contribution of conserved amino acid to ATGL inhibition. Our site directed mutagenesis and truncation studies give insights in the protein-protein interaction on a per-residue level. We determine that the minimal sequence required for ATGL inhibition ranges from amino acids 20 to 44. Residues Y27, V28, G30, A34 G37, V39 or L42 within this sequence play a substantial role in ATGL inhibition. Furthermore, we show that unspecific interactions of the N-terminal part (amino acids 20-27) of the minimal sequence facilitate the interaction to ATGL. Our studies also demonstrate that full-length G0S2 shows higher tolerance to specific single amino acid exchanges in the hydrophobic region due to the stronger contributions of unspecific interactions. However, exchanges of more than one amino-acid in the hydrophobic region also result in the loss of function as ATGL inhibitor even in the full-length protein.

Lipid droplets associated perilipins protein insights into finding a therapeutic target approach to cure non-alcoholic fatty liver disease (NAFLD)

Background

Non-alcoholic fatty liver disease (NAFLD) is now the most common form of chronic liver disease in the world, and it’s linked to a slew of other risk factors including diabetes, obesity, dysbiosis and inflammatory bowel disease. More than 30 years ago, a patient was diagnosed with fatty liver with excessive fat accumulation in hepatocytes, a disorder known as hepatosteatosis. There will be no promising therapeutic medicines available from 1980 to 2021 which can reverse the fatty liver to normal liver state. In this review, we highlighted on lipid droplet associated protein which play a major role in accumulation of fat in liver cells and how these cellular pathway could be a promising therapeutic approach to treat the fatty liver disease.

Main body

Over the last few decades, Western countries follow a high-fat diet and change their lifestyle pattern due to certain metabolic disorders prevalence rate is very high all over the world. NAFLD is a major health issue and burden globally nowadays. Researchers are trying to find out the potential therapeutic target to combat the disease. The exact pathophysiology of the disease is still unclear. In the present decades. There is no Food and Drug Administration approved drugs are available to reverse the chronic condition of the disease. Based on literature survey, lipid droplets and their associated protein like perilipins play an eminent role in body fat regulation. In this review, we explain all types of perilipins such as perilipin1-5 (PLIN1-5) and their role in the pathogenesis of fatty liver which will be helpful to find the novel pharmacological target to treat the fatty liver.

Conclusion

In this review, majorly focussed on how fat is get deposited into hepatocytes follow the cellular signalling involved during lipid droplet biogenesis and leads to NAFLD. However, up to date still there mechanism of action is unclear. In this review, we hypothesized that lipid droplets associated proteins like perilipins could be better pharmacological target to reverse the chronic stage of fatty liver disease and how these lipid droplets associated proteins hide a clue to maintain the normal lipid homeostasis in the human body.

Lipolysis: cellular mechanisms for lipid mobilization from fat stores

The perception that intracellular lipolysis is a straightforward process that releases fatty acids from fat stores in adipose tissue to generate energy has experienced major revisions over the last two decades. The discovery of new lipolytic enzymes and coregulators, the demonstration that lipophagy and lysosomal lipolysis contribute to the degradation of cellular lipid stores and the characterization of numerous factors and signalling pathways that regulate lipid hydrolysis on transcriptional and post-transcriptional levels have revolutionized our understanding of lipolysis. In this review, we focus on the mechanisms that facilitate intracellular fatty-acid mobilization, drawing on canonical and noncanonical enzymatic pathways. We summarize how intracellular lipolysis affects lipid-mediated signalling, metabolic regulation and energy homeostasis in multiple organs. Finally, we examine how these processes affect pathogenesis and how lipolysis may be targeted to potentially prevent or treat various diseases.

Hypoxia, hypoxia-inducible gene 2 (HIG2)/HILPDA, and intracellular lipolysis in cancer

Tumor tissues are chronically exposed to hypoxia owing to aberrant vascularity. Hypoxia induces metabolic alterations in cancer, thereby promoting aggressive malignancy and metastasis. While previous efforts largely focused on adaptive responses in glucose and glutamine metabolism, recent studies have begun to yield important insight into the hypoxic regulation of lipid metabolic reprogramming in cancer. Emerging evidence points to lipid droplet (LD) accumulation as a hallmark of hypoxic cancer cells. One critical underlying mechanism involves the inhibition of adipose triglyceride lipase (ATGL)-mediated intracellular lipolysis by a small protein encoded by hypoxia-inducible gene 2 (HIG2), also known as hypoxia inducible lipid droplet associated (HILPDA). In this review we summarize and discuss recent key findings on hypoxia-dependent regulation of metabolic adaptations especially lipolysis in cancer. We also pose several questions and hypotheses pertaining to the metabolic impact of lipolytic regulation in cancer under hypoxia and during hypoxia-reoxygenation transition.

Updating Phospholipase A2 Biology

The phospholipase A2 (PLA2) superfamily contains more than 50 enzymes in mammals that are subdivided into several distinct families on a structural and biochemical basis. In principle, PLA2 has the capacity to hydrolyze the sn-2 position of glycerophospholipids to release fatty acids and lysophospholipids, yet several enzymes in this superfamily catalyze other reactions rather than or in addition to the PLA2 reaction. PLA2 enzymes play crucial roles in not only the production of lipid mediators, but also membrane remodeling, bioenergetics, and body surface barrier, thereby participating in a number of biological events. Accordingly, disturbance of PLA2-regulated lipid metabolism is often associated with various diseases. This review updates the current state of understanding of the classification, enzymatic properties, and biological functions of various enzymes belonging to the PLA2 superfamily, focusing particularly on the novel roles of PLA2s in vivo.

Current Approaches and Applications in Avian Genome Editing

Advances in genome-editing technologies and sequencing of animal genomes enable researchers to generate genome-edited (GE) livestock as valuable animal models that benefit biological researches and biomedical and agricultural industries. As birds are an important species in biology and agriculture, their genome editing has gained significant interest and is mainly performed by using a primordial germ cell (PGC)-mediated method because pronuclear injection is not practical in the avian species. In this method, PGCs can be isolated, cultured, genetically edited in vitro, and injected into a recipient embryo to produce GE offspring. Recently, a couple of GE quail have been generated by using the newly developed adenovirus-mediated method. Without technically required in vitro procedures of the PGC-mediated method, direct injection of adenovirus into the avian blastoderm in the freshly laid eggs resulted in the production of germ-line chimera and GE offspring. As more approaches are available in avian genome editing, avian research in various fields will progress rapidly. In this review, we describe the development of avian genome editing and scientific and industrial applications of GE avian species.

Assessment of Periprostatic and Subcutaneous Adipose Tissue Lipolysis and Adipocyte Size from Men with Localized Prostate Cancer

The prostate is surrounded by periprostatic adipose tissue (PPAT), the thickness of which has been associated with more aggressive prostate cancer (PCa). There are limited data regarding the functional characteristics of PPAT, how it compares to subcutaneous adipose tissue (SAT), and whether in a setting of localized PCa, these traits are altered by obesity or disease aggressiveness. PPAT and SAT were collected from 60 men (age: 42–78 years, BMI: 21.3–35.6 kg/m²) undergoing total prostatectomy for PCa. Compared to SAT, adipocytes in PPAT were smaller, had the same basal rates of fatty acid release (lipolysis) yet released less polyunsaturated fatty acid species, and were more sensitive to isoproterenol-stimulated lipolysis. Basal lipolysis of PPAT was increased in men diagnosed with less aggressive PCa (Gleason score (GS) ≤ 3 + 4) compared to men with more aggressive PCa (GS ≥ 4 + 3) but no other measured adipocyte parameters related to PCa aggressiveness. Likewise, there was no difference in PPAT lipid biology between lean and obese men. In conclusion, lipid biological features of PPAT do differ from SAT; however, we did not observe any meaningful difference in ex vivo PPAT biology that is associated with PCa aggressiveness or obesity. As such, our findings do not support a relationship between altered PCa behavior in obese men and the metabolic reprogramming of PPAT.

Metabolic Reprogramming of Macrophages in Atherosclerosis: Is It All about Cholesterol?

Hypercholesterolemia contributes to the chronic inflammatory response during the progression of atherosclerosis, in part by favoring cholesterol loading in macrophages and other immune cells. However, macrophages encounter a substantial amount of other lipids and nutrients after ingesting atherogenic lipoprotein particles or clearing apoptotic cells, increasing their metabolic load and impacting their behavior during atherosclerosis plaque progression. This review examines whether and how fatty acids and glucose shape the cellular metabolic reprogramming of macrophages in atherosclerosis to modulate the onset phase of inflammation and the later resolution stage, in which the balance is tipped toward tissue repair.

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".

Changes in adipose tissue lipolysis gene expression and insulin sensitivity after weight loss

OBJECTIVE

Insulin resistance is a major pathophysiological link between obesity and its metabolic complications. Weight loss (WL) is an effective tool to prevent obesity-related diseases; however, the mechanisms of an improvement in insulin sensitivity (IS) after weight-reducing interventions are not completely understood. The aim of the present study was to analyze the relationships between IS and adipose tissue (AT) expression of the genes involved in the regulation of lipolysis in obese subjects after WL.

METHODS

Fifty-two obese subjects underwent weight-reducing dietary intervention program. The control group comprised 20 normal-weight subjects, examined at baseline only. Hyperinsulinemic-euglycemic clamp and s.c. AT biopsy with subsequent gene expression analysis were performed before and after the program.

RESULTS

AT expression of genes encoding lipases (PNPLA2, LIPE and MGLL) and lipid-droplet proteins enhancing (ABHD5) and inhibiting lipolysis (PLIN1 and CIDEA) were decreased in obese individuals in comparison with normal-weight individuals. The group of 38 obese participants completed dietary intervention program and clamp studies, which resulted in a significant WL and an improvement in mean IS. However, in nine subjects from this group IS did not improve in response to WL. AT expression of PNPLA2, LIPE and PLIN1 increased only in the group without IS improvement.

CONCLUSIONS

Excessive lipolysis may prevent an improvement in IS during WL. The change in AT PNPLA2 and LIPE expression was a negative predictor of the change in IS after WL.

In vivo real-time ATP imaging in zebrafish hearts reveals G0s2 induces ischemic tolerance

Most eukaryotic cells generate adenosine triphosphate (ATP) through the oxidative phosphorylation system (OXPHOS) to support cellular activities. In cultured cell-based experiments, we recently identified the hypoxia-inducible protein G0/G1 switch gene 2 (G0s2) as a positive regulator of OXPHOS, and showed that G0s2 protects cultured cardiomyocytes from hypoxia. In this study, we examined the in vivo protective role of G0s2 against hypoxia by generating both loss-of-function and gain-of-function models of g0s2 in zebrafish. Zebrafish harboring transcription activator-like effector nuclease (TALEN)-mediated knockout of g0s2 lost hypoxic tolerance. Conversely, cardiomyocyte-specific transgenic zebrafish hearts exhibited strong tolerance against hypoxia. To clarify the mechanism by which G0s2 protects cardiac function under hypoxia, we introduced a mitochondrially targeted FRET-based ATP biosensor into zebrafish heart to visualize ATP dynamics in in vivo beating hearts. In addition, we employed a mosaic overexpression model of g0s2 to compare the contraction and ATP dynamics between g0s2-expressing and non-expressing cardiomyocytes, side-by-side within the same heart. These techniques revealed that g0s2-expressing cardiomyocyte populations exhibited preserved contractility coupled with maintained intra-mitochondrial ATP concentrations even under hypoxic condition. Collectively, these results demonstrate that G0s2 provides ischemic tolerance in vivo by maintaining ATP production, and therefore represents a promising therapeutic target for hypoxia-related diseases.

Genetic Programs Driving Oncogenic Transformation: Lessons from in Vitro Models

Cancer complexity relies on the intracellular pleiotropy of oncogenes/tumor suppressors and in the strong interplay between tumors and micro- and macro-environments. Here we followed a reductionist approach, by analyzing the transcriptional adaptations induced by three oncogenes (RAS, MYC, and HDAC4) in an isogenic transformation process. Common pathways, in place of common genes became dysregulated. From our analysis it emerges that, during the process of transformation, tumor cells cultured in vitro prime some signaling pathways suitable for coping with the blood supply restriction, metabolic adaptations, infiltration of immune cells, and for acquiring the morphological plasticity needed during the metastatic phase. Finally, we identified two signatures of genes commonly regulated by the three oncogenes that successfully predict the outcome of patients affected by different cancer types. These results emphasize that, in spite of the heterogeneous mutational burden among different cancers and even within the same tumor, some common hubs do exist. Their location, at the intersection of the various signaling pathways, makes a therapeutic approach exploitable.

G0/G1 Switch 2 Induces Cell Survival and Metastasis through Integrin-Mediated Signal Transduction in Human Invasive Breast Cancer Cells

Human breast cancer cell line, MDA-MB-231, is highly invasive and aggressive, compared to less invasive cell line, MCF-7. To explore the genes that might influence the malignancy of MDA-MB-231, DNA microarray analysis was performed. The results showed that G0/G1 switch 2 (G0S2) was one of the most highly expressed genes among the genes upregulated in MDA-MB-231. Although G0S2 acts as a direct inhibitor of adipose triglyceride lipase, action of G0S2 in cancer progression is not yet understood. To investigate whether G0S2 affects invasiveness of MDA-MB-231 cells, G0S2 expression was inhibited using siRNA, which led to decreased cell proliferation, migration, and invasion of MDA-MB-231 cells. Consequently, G0S2 inhibition inactivated integrinregulated FAK-Src signaling, which promoted Hippo signaling and inactivated ERK1/2 signaling. In addition, G0S2 downregulation decreased β-catenin expression, while E-cadherin expression was increased. It was demonstrated for the first time that G0S2 mediates the Hippo pathway and induces epithelial to mesenchymal transition (EMT). Taken together, our results suggest that G0S2 is a major factor contributing to cell survival and metastasis of MDA-MB-231 cells.

High doses of ANP and BNP exacerbate lipolysis in humans and the lipolytic effect of BNP is associated with cardiac triglyceride content in pigs

Drugs facilitating the cardioprotective effects of natriuretic peptides are introduced in heart failure treatment. ANP and BNP also stimulate lipolysis and increase circulating concentrations of free fatty acids (FFAs); an aspect, however, thought to be confined to primates. We examined the lipolytic effect of natriuretic peptide infusion in healthy young men and evaluated the effect in a porcine model of myocardial ischemia and reperfusion. Six young healthy normotensive men underwent infusion with ANP, BNP, or CNP for 20 min. Blood samples were collected before, during, and after infusion for measurement of FFAs. In a porcine model of myocardial ischemia and reperfusion, animals were infused for 3 h with either BNP (n = 7) or saline (n = 5). Blood samples were collected throughout the infusion period, and cardiac tissue was obtained after infusion for lipid analysis. In humans, ANP infusion dose-dependently increased the FFA concentration in plasma 2.5-10-fold (baseline vs. 0.05 μg/kg/min P < 0.002) and with BNP 1.6-3.5-fold (P = 0.001, baseline vs. 0.02 μg/kg/min) 30 min after initiation of infusion. Infusion of CNP did not affect plasma FFA. In pigs, BNP infusion induced a 3.5-fold increase in plasma FFA (P < 0.0001), which remained elevated throughout the infusion period. Triglyceride content in porcine right cardiac ventricle tissue increased ∼5.5 fold in animals infused with BNP (P = 0.02). Natriuretic peptide infusion has similar lipolytic activity in human and pig. Our data suggest that short-term infusion increases the cardiac lipid content, and that the pig is a suitable model for studies of long-term effects mediated by natriuretic peptides.

Constitutive P2Y2 receptor activity regulates basal lipolysis in human adipocytes

White adipocytes are key regulators of metabolic homeostasis, which release stored energy as free fatty acids via lipolysis. Adipocytes possess both basal and stimulated lipolytic capacity, but limited information exists regarding the molecular mechanisms that regulate basal lipolysis. Here, we describe a mechanism whereby autocrine purinergic signalling and constitutive P2Y₂ receptor activation suppresses basal lipolysis in primary human in vitro-differentiated adipocytes. We found that human adipocytes possess cytoplasmic Ca²⁺ tone due to ATP secretion and constitutive P2Y₂ receptor activation. Pharmacological antagonism or knockdown of P2Y₂ receptors increases intracellular cAMP levels and enhances basal lipolysis. P2Y₂ receptor antagonism works synergistically with phosphodiesterase inhibitors in elevating basal lipolysis, but is dependent upon adenylate cyclase activity. Mechanistically, we suggest that the increased Ca²⁺ tone exerts an anti-lipolytic effect by suppression of Ca²⁺-sensitive adenylate cyclase isoforms. We also observed that acute enhancement of basal lipolysis following P2Y₂ receptor antagonism alters the profile of secreted adipokines leading to longer-term adaptive decreases in basal lipolysis. Our findings demonstrate that basal lipolysis and adipokine secretion are controlled by autocrine purinergic signalling in human adipocytes.

Metabolite and lipoprotein responses and prediction of weight gain during breast cancer treatment

Background

Breast cancer treatment has metabolic side effects, potentially affecting risk of cardiovascular disease (CVD) and recurrence. We aimed to compare alterations in serum metabolites and lipoproteins during treatment between recipients and non-recipients of chemotherapy, and describe metabolite profiles associated with treatment-related weight gain.

Methods

This pilot study includes 60 stage I/II breast cancer patients who underwent surgery and were treated according to national guidelines. Serum sampled pre-surgery and after 6 and 12 months was analysed by MR spectroscopy and mass spectrometry. In all, 170 metabolites and 105 lipoprotein subfractions were quantified.

Results

The metabolite and lipoprotein profiles of chemotherapy recipients and non-recipients changed significantly 6 months after surgery (p < 0.001). Kynurenine, the lipid signal at 1.55–1.60 ppm, ADMA, 2 phosphatidylcholines (PC aa C38:3, PC ae C42:1), alpha-aminoadipic acid, hexoses and sphingolipids were increased in chemotherapy recipients after 6 months. VLDL and small dense LDL increased after 6 months, while HDL decreased, with triglyceride enrichment in HDL and LDL. At baseline, weight gainers had less acylcarnitines, phosphatidylcholines, lyso-phosphatidylcholines and sphingolipids, and showed an inflammatory lipid profile.

Conclusion

Chemotherapy recipients exhibit metabolic changes associated with inflammation, altered immune response and increased risk of CVD. Altered lipid metabolism may predispose for treatment-related weight gain.

Disruption of G0/G1 switch gene 2 ( G0S2) reduced abdominal fat deposition and altered fatty acid composition in chicken

Chicken as a food source is one of the most widespread domestic animals, and it has been used extensively as a research model. The clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9) system is the most efficient and reliable tool for precise genome-targeted modification and has generated considerable excitement for industrial applications, as well as biologic science. Unlike in mammals, germline-transmittable primordial germ cells (PGCs) in chicken were used as an alternative strategy for the production of genetically altered chickens. Here, by combining the CRISPR-Cas9 platform and germ cell-mediated germline transmission, we generated G₀/G₁ switch gene 2 ( G0S2) knockout (KO) chickens, and G0S2 null KO chickens showed a dramatic reduction of abdominal fat deposition without affecting other economic traits. Additionally, G0S2 null KO chickens had altered fatty acid compositions in their blood and abdominal fat compared with wild-type chickens under normal dietary conditions. The global mRNA sequencing data showed that G0S2 disruption in chickens would activate the adipose tissue-specific peroxisomal oxidation pathway, and enoyl-coenzyme A (CoA), hydratase/3-hydroxyacyl CoA dehydrogenase might be a target molecule in metabolic homeostasis in the chicken adipose tissue. Our results demonstrate that the CRISPR-Cas9 system with chicken PGCs can facilitate the production of specific genome-edited chickens for practical applications, as well as basic research.-Park, T. S., Park, J., Lee, J. H., Park, J.-W., Park, B.-C. Disruption of G₀/G₁ switch gene 2 ( G0S2) reduced abdominal fat deposition and altered fatty acid composition in chicken.

Adipose KLF15 Controls Lipid Handling to Adapt to Nutrient Availability

Adipose tissue stores energy in the form of triglycerides. The ability to regulate triglyceride synthesis and breakdown based on nutrient status (e.g., fed versus fasted) is critical for physiological homeostasis and dysregulation of this process can contribute to metabolic disease. Whereas much is known about hormonal control of this cycle, transcriptional regulation is not well understood. Here, we show that the transcription factor Kruppel-like factor 15 (KLF15) is critical for the control of adipocyte lipid turnover. Mice lacking Klf15 in adipose tissue (AK15KO) display decreased adiposity and are protected from diet-induced obesity. Mechanistic studies suggest that adipose KLF15 regulates key genes of triglyceride synthesis and inhibits lipolytic action, thereby promoting lipid storage in an insulin-dependent manner. Finally, AK15KO mice demonstrate accelerated lipolysis and altered systemic energetics (e.g., locomotion, ketogenesis) during fasting conditions. Our study identifies adipose KLF15 as an essential regulator of adipocyte lipid metabolism and systemic energy balance.

Pharmacological intervention of liver triacylglycerol lipolysis: The good, the bad and the ugly

Excessive triacylglycerol (TG) accumulation is the distinctive feature of obesity. In the liver, sustained TG accretion leads to nonalcoholic fatty liver disease (NAFLD), eventually progressing to non-alcoholic steatohepatitis (NASH) and cirrhosis, which is associated with complications including hepatic failure, hepatocellular carcinoma and death. Pharmacological interventions are actively pursued to prevent lipid accumulation in hepatocytes and, therefore, to ameliorate the associated pathophysiological conditions. Here, we sought to provide an overview of the pharmacological approaches to up- or downregulate the expression and activities of the enzymes involved in hepatic TG hydrolysis. Fatty acids (FA) released by hydrolysis of hepatic TG can be used for β-oxidation, signaling, and for very low-density lipoprotein (VLDL)-TG synthesis. Originally, lipolysis was believed to be centered in the adipose and to be catalyzed by only two lipases, hormone-sensitive lipase (HSL) and monoacylglycerol lipase (MAGL). However, genetic ablation of HSL expression in mice failed to erase TG hydrolysis in adipocytes leading to the identification of a third lipase termed adipose triglyceride lipase (ATGL). Although these three enzymes are considered to be the main players governing lipolysis in the adipocyte, other lipolytic enzymes have been described to contribute to hepatic TG metabolism. These include adiponutrin/patatin-like phospholipase domain containing 3 (PNPLA3), some members of the carboxylesterase family (CES/Ces), arylacetamide deacetylase (AADAC), lysosomal acid lipase (LAL) and hepatic lipase (HL). This review highlights the consequences of pharmacological interventions of liver lipases that degrade TG in cytosolic lipid droplets, in the endoplasmic reticulum, in the late endosomes/lysosomes and along the secretory route.

Cytosolic lipolysis and lipophagy: two sides of the same coin

Fatty acids are the most efficient substrates for energy production in vertebrates and are essential components of the lipids that form biological membranes. Synthesis of triacylglycerols from non-esterified free fatty acids (FFAs) combined with triacylglycerol storage represents a highly efficient strategy to stockpile FFAs in cells and prevent FFA-induced lipotoxicity. Although essentially all vertebrate cells have some capacity to store and utilize triacylglycerols, white adipose tissue is by far the largest triacylglycerol depot and is uniquely able to supply FFAs to other tissues. The release of FFAs from triacylglycerols requires their enzymatic hydrolysis by a process called lipolysis. Recent discoveries thoroughly altered and extended our understanding of lipolysis. This Review discusses how cytosolic 'neutral' lipolysis and lipophagy, which utilizes 'acid' lipolysis in lysosomes, degrade cellular triacylglycerols as well as how these pathways communicate, how they affect lipid metabolism and energy homeostasis and how their dysfunction affects the pathogenesis of metabolic diseases. Answers to these questions will likely uncover novel strategies for the treatment of prevalent metabolic diseases.

Dynamic transcriptome and DNA methylome analyses on longissimus dorsi to identify genes underlying intramuscular fat content in pigs

Background

The intramuscular fat content (IMF) refers to the amount of fat within muscles, including the sum of phospholipids mainly found in cell membranes, triglycerides and cholesterol, and is determined both by hyperplasia and hypertrophy of adipocyte during the development of pigs. The IMF content is an important economic trait that is genetically controlled by multiple genes. The Laiwu pig is an indigenous fatty pig breed distributed in North China, characterized by excessively higher level of IMF content (9%~12%), therefore, is suitable for the identification of genes controlling IMF variations. To identify genes underlying IMF deposition, we performed genome-wide transcriptome and methylome analyses on longissimus dorsi (LD) muscle in Laiwu pigs across four developmental stages.

Results

A total of 22,524 expressed genes were detected and 1158 differentially expressed genes (DEGs) were hierarchically clustered in the LD muscle over four developmental stages from 60 d to 400 d. These genes were significantly clustered into four temporal expression profiles, and genes participating in fat cell differentiation and lipid biosynthesis processes were identified. From 120 d to 240 d, the period with the maximum IMF deposition rate, the lipid biosynthesis related genes (FOSL1, FAM213B and G0S2), transcription factors (TFs) (EGR1, KLF5, SREBF2, TP53 and TWIST1) and enriched pathways (steroid biosynthesis and fatty acid biosynthesis) were revealed; and fat biosynthesis relevant genes showing differences in DNA methylation in gene body or intergenic region were detected, such as FASN, PVALB, ID2, SH3PXD2B and EGR1.

Conclusions

This study provides a comprehensive landscape of transcriptome of the LD muscle in Laiwu pigs ranging from 60 to 400 days old, and methylome of the LD muscle in 120 d and 240 d Laiwu pigs. A set of candidate genes and TFs involved in fat biosynthesis process were identified, which were probably responsible for IMF deposition. The results from this study would provide a reference for the identification of genes controlling IMF variation, and for exploring molecular mechanisms underlying IMF deposition in pigs.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4201-9) contains supplementary material, which is available to authorized users.

Fat Cell and Fatty Acid Turnover in Obesity

The ratio of free fatty acid (FFA) turnover decreases significantly with the expansion of white adipose tissue. Adipose tissue and dietary saturated fatty acid levels significantly correlate with an increase in fat cell size and number. Inhibition of adipose triglyceride lipase leads to an accumulation of triglyceride, whereas inhibition of hormone-sensitive lipase leads to the accumulation of diacylglycerol. The G0/G1 switch gene 2 increases lipid content in adipocytes and promotes adipocyte hypertrophy through the restriction of triglyceride turnover. Excess triacylglycerols (TAGs), sterols and sterol esters are surrounded by the phospholipid monolayer surface and form lipid droplets. Following the release of lipid droplets from endoplasmic reticulum, cytoplasmic lipid droplets increase their volume either by local TAG synthesis or by homotypic fusion. The number and the size of lipid droplet distribution is correlated with obesity. Obesity-associated adipocyte death exhibits feature of necrosis-like programmed cell death. NOD-like receptors family pyrin domain containing 3 (NLRP3) inflammasome-dependent caspase-1 activation in hypertrophic adipocytes induces obese adipocyte death by pyroptosis. Actually adipocyte death may be a prerequisite for the transition from hypertrophic to hyperplastic obesity. Major transcriptional factors, CCAAT/enhancer-binding proteins beta and delta, play a central role in the subsequent induction of critical regulators, peroxisome-proliferator-activated receptor gamma, CCAAT/enhancer-binding protein alpha and sterol regulatory element-binding protein 1, in the transcriptional control of adipogenesis in obesity.Collectively, in this chapter the concept of adipose tissue remodeling in response to adipocyte death or adipogenesis, and the complexity of lipid droplet interactions with the other cellular organelles are reviewed. Furthermore, in addition to lipid droplet growth, the functional link between the adipocyte-specific lipid droplet-associated protein and fatty acid turn-over is also debated.

G0S2: A small giant controller of lipolysis and adipose-liver fatty acid flux

The discovery of adipose triglyceride lipase (ATGL) and its coactivator comparative gene identification-58 (CGI-58) provided a major paradigm shift in the understanding of intracellular lipolysis in both adipocytes and nonadipocyte cells. The subsequent discovery of G0/G1 switch gene 2 (G0S2) as a potent endogenous inhibitor of ATGL revealed a unique mechanism governing lipolysis and fatty acid (FA) availability. G0S2 is highly conserved in vertebrates, and exhibits cyclical expression pattern between adipose tissue and liver that is critical to lipid flux and energy homeostasis in these two tissues. Biochemical and cell biological studies have demonstrated that a direct interaction with ATGL mediates G0S2's inhibitory effects on lipolysis and lipid droplet degradation. In this review we examine evidence obtained from recent in vitro and in vivo studies that lends support to the proof-of-principle concept that G0S2 functions as a master regulator of tissue-specific balance of TG storage vs. mobilization, partitioning of metabolic fuels between adipose and liver, and the whole-body adaptive energy response. This article is part of a Special Issue entitled: Recent Advances in Lipid Droplet Biology edited by Rosalind Coleman and Matthijs Hesselink.

Adipocyte Glucocorticoid Receptor Deficiency Attenuates Aging- and HFD-Induced Obesity and Impairs the Feeding-Fasting Transition

Glucocorticoids (GCs) are important regulators of systemic energy metabolism, and aberrant GC action is linked to metabolic dysfunctions. Yet, the extent to which normal and pathophysiological energy metabolism depend on the GC receptor (GR) in adipocytes remains unclear. Here, we demonstrate that adipocyte GR deficiency in mice significantly impacts systemic metabolism in different energetic states. Plasma metabolomics and biochemical analyses revealed a marked global effect of GR deficiency on systemic metabolite abundance and, thus, substrate partitioning in fed and fasted states. This correlated with a decreased lipolytic capacity of GR-deficient adipocytes under postabsorptive and fasting conditions, resulting from impaired signal transduction from β-adrenergic receptors to adenylate cyclase. Upon prolonged fasting, the impaired lipolytic response resulted in abnormal substrate utilization and lean mass wasting. Conversely, GR deficiency attenuated aging-/diet-associated obesity, adipocyte hypertrophy, and liver steatosis. Systemic glucose tolerance was improved in obese GR-deficient mice, which was associated with increased insulin signaling in muscle and adipose tissue. We conclude that the GR in adipocytes exerts central but diverging roles in the regulation of metabolic homeostasis depending on the energetic state. The adipocyte GR is indispensable for the feeding-fasting transition but also promotes adiposity and associated metabolic disorders in fat-fed and aged mice.

Regulation of G0/G1 Switch Gene 2 (G0S2) Protein Ubiquitination and Stability by Triglyceride Accumulation and ATGL Interaction

Intracellular triglyceride (TG) hydrolysis or lipolysis is catalyzed by the key intracellular triglyceride hydrolase, adipose triglyceride lipase (ATGL). The G0/G1 Switch Gene 2 (G0S2) was recently identified as the major selective inhibitor of ATGL and its hydrolase function. Since G0S2 levels are dynamically linked and rapidly responsive to nutrient status or metabolic requirements, the identification of its regulation at the protein level is of significant value. Earlier evidence from our laboratory demonstrated that G0S2 is a short-lived protein degraded through the proteasomal pathway. However, little is currently known regarding the underlying mechanisms. In the current study we find that 1) protein degradation is initiated by K48-linked polyubiquitination of the lysine- 25 in G0S2; and 2) G0S2 protein is stabilized in response to ATGL expression and TG accumulation. Mutation of lysine-25 of G0S2 abolished ubiquitination and increased protein stability. More importantly, G0S2 was stabilized via different mechanisms in the presence of ATGL vs. in response to fatty acid (FA)-induced TG accumulation. Furthermore, G0S2 protein but not mRNA levels were reduced in the adipose tissue of ATGL-deficient mice, corroborating the involvement of ATGL in the stabilization of G0S2. Taken together our data illustrate for the first time a crucial multifaceted mechanism for the stabilization of G0S2 at the protein level.

G0/G1 Switch Gene 2 controls adipose triglyceride lipase activity and lipid metabolism in skeletal muscle

OBJECTIVE

Recent data suggest that adipose triglyceride lipase (ATGL) plays a key role in providing energy substrate from triglyceride pools and that alterations of its expression/activity relate to metabolic disturbances in skeletal muscle. Yet little is known about its regulation. We here investigated the role of the protein G0/G1 Switch Gene 2 (G0S2), recently described as an inhibitor of ATGL in white adipose tissue, in the regulation of lipolysis and oxidative metabolism in skeletal muscle.

METHODS

We first examined G0S2 protein expression in relation to metabolic status and muscle characteristics in humans. We next overexpressed and knocked down G0S2 in human primary myotubes to assess its impact on ATGL activity, lipid turnover and oxidative metabolism, and further knocked down G0S2 in vivo in mouse skeletal muscle.

RESULTS

G0S2 protein is increased in skeletal muscle of endurance-trained individuals and correlates with markers of oxidative capacity and lipid content. Recombinant G0S2 protein inhibits ATGL activity by about 40% in lysates of mouse and human skeletal muscle. G0S2 overexpression augments (+49%, p < 0.05) while G0S2 knockdown strongly reduces (-68%, p < 0.001) triglyceride content in human primary myotubes and mouse skeletal muscle. We further show that G0S2 controls lipolysis and fatty acid oxidation in a strictly ATGL-dependent manner. These metabolic adaptations mediated by G0S2 are paralleled by concomitant changes in glucose metabolism through the modulation of Pyruvate Dehydrogenase Kinase 4 (PDK4) expression (5.4 fold, p < 0.001). Importantly, downregulation of G0S2 in vivo in mouse skeletal muscle recapitulates changes in lipid metabolism observed in vitro.

CONCLUSION

Collectively, these data indicate that G0S2 plays a key role in the regulation of skeletal muscle ATGL activity, lipid content and oxidative metabolism.

G0S2 Suppresses Oncogenic Transformation by Repressing a MYC-Regulated Transcriptional Program

Methylation-mediated silencing of G0-G1 switch gene 2 (G0S2) has been detected in a variety of solid tumors, whereas G0S2 induction is associated with remissions in patients with acute promyelocytic leukemia, implying that G0S2 may possess tumor suppressor activity. In this study, we clearly demonstrate that G0S2 opposes oncogene-induced transformation using G0s2-null immortalized mouse embryonic fibroblasts (MEF). G0s2-null MEFs were readily transformed with HRAS or EGFR treatment compared with wild-type MEFs. Importantly, restoration of G0S2 reversed HRAS-driven transformation. G0S2 is known to regulate fat metabolism by attenuating adipose triglyceride lipase (ATGL), but repression of oncogene-induced transformation by G0S2 was independent of ATGL inhibition. Gene expression analysis revealed an upregulation of gene signatures associated with transformation, proliferation, and MYC targets in G0s2-null MEFs. RNAi-mediated ablation and pharmacologic inhibition of MYC abrogated oncogene-induced transformation of G0s2-null MEFs. Furthermore, we found that G0S2 was highly expressed in normal breast tissues compared with malignant tissue. Intriguingly, high levels of G0S2 were also associated with a decrease in breast cancer recurrence rates, especially in estrogen receptor-positive subtypes, and overexpression of G0S2 repressed the proliferation of breast cancer cells in vitro. Taken together, these findings indicate that G0S2 functions as a tumor suppressor in part by opposing MYC activity, prompting further investigation of the mechanisms by which G0S2 silencing mediates MYC-induced oncogenesis in other malignancies.

Regulation of G0/G1 switch gene 2 (G0S2) expression in human adipose tissue

The G0/G1 switch gene 2 (G0S2) protein attenuated adipose triglyceride lipase (ATGL) activity and decreased lipolysis in rodent and human adipocytes. We hypothesized that G0S2 mRNA expression in human adipose tissue is influenced by depot, adipocyte size, body weight and caloric intake. Adipose tissue samples were obtained during abdominal surgery and by needle biopsy before and 3 h after an extended glucose load in lean subjects. G0S2 mRNA was 7× higher expressed in mature human adipocytes compared to the stromavascular fraction. Cell size inversely correlated with G0S2 mRNA expression in both, subcutaneous and omental adipose depots. G0S2 mRNA expression was 75% higher in subcutaneous compared to omental adipose tissue. Obesity was associated with lower G0S2 mRNA expression in subcutaneous adipose tissue. Acute glucose ingestion after an overnight fast did not significantly increase G0S2 expression in subcutaneous adipose tissue. In conclusion, differences in G0S2 expression may explain depot-specific and obesity-associated differences in lipolysis on the molecular level.

G0/G1 Switch Gene 2 Regulates Cardiac Lipolysis

The anabolism and catabolism of myocardial triacylglycerol (TAG) stores are important processes for normal cardiac function. TAG synthesis detoxifies and stockpiles fatty acids to prevent lipotoxicity, whereas TAG hydrolysis (lipolysis) remobilizes fatty acids from endogenous storage pools as energy substrates, signaling molecules, or precursors for complex lipids. This study focused on the role of G0/G1 switch 2 (G0S2) protein, which was previously shown to inhibit the principal TAG hydrolase adipose triglyceride lipase (ATGL), in the regulation of cardiac lipolysis. Using wild-type and mutant mice, we show the following: (i) G0S2 is expressed in the heart and regulated by the nutritional status with highest expression levels after re-feeding. (ii) Cardiac-specific overexpression of G0S2 inhibits cardiac lipolysis by direct protein-protein interaction with ATGL. This leads to severe cardiac steatosis. The steatotic hearts caused by G0S2 overexpression are less prone to fibrotic remodeling or cardiac dysfunction than hearts with a lipolytic defect due to ATGL deficiency. (iii) Conversely to the phenotype of transgenic mice, G0S2 deficiency results in a de-repression of cardiac lipolysis and decreased cardiac TAG content. We conclude that G0S2 acts as a potent ATGL inhibitor in the heart modulating cardiac substrate utilization by regulating cardiac lipolysis.

Fasting-induced G0/G1 switch gene 2 and FGF21 expression in the liver are under regulation of adipose tissue derived fatty acids

BACKGROUND & AIMS

Adipose tissue (AT)-derived fatty acids (FAs) are utilized for hepatic triacylglycerol (TG) generation upon fasting. However, their potential impact as signaling molecules is not established. Herein we examined the role of exogenous AT-derived FAs in the regulation of hepatic gene expression by investigating mice with a defect in AT-derived FA supply to the liver.

METHODS

Plasma FA levels, tissue TG hydrolytic activities and lipid content were determined in mice lacking the lipase co-activator comparative gene identification-58 (CGI-58) selectively in AT (CGI-58-ATko) applying standard protocols. Hepatic expression of lipases, FA oxidative genes, transcription factors, ER stress markers, hormones and cytokines were determined by qRT-PCR, Western blotting and ELISA.

RESULTS

Impaired AT-derived FA supply upon fasting of CGI-58-ATko mice causes a marked defect in liver PPARα-signaling and nuclear CREBH translocation. This severely reduced the expression of respective target genes such as the ATGL inhibitor G0/G1 switch gene-2 (G0S2) and the endocrine metabolic regulator FGF21. These changes could be reversed by lipid administration and raising plasma FA levels. Impaired AT-lipolysis failed to induce hepatic G0S2 expression in fasted CGI-58-ATko mice leading to enhanced ATGL-mediated TG-breakdown strongly reducing hepatic TG deposition. On high fat diet, impaired AT-lipolysis counteracts hepatic TG accumulation and liver stress linked to improved systemic insulin sensitivity.

CONCLUSIONS

AT-derived FAs are a critical regulator of hepatic fasting gene expression required for the induction of G0S2-expression in the liver to control hepatic TG-breakdown. Interfering with AT-lipolysis or hepatic G0S2 expression represents an effective strategy for the treatment of hepatic steatosis.

Cidea improves the metabolic profile through expansion of adipose tissue

In humans, Cidea (cell death-inducing DNA fragmentation factor alpha-like effector A) is highly but variably expressed in white fat, and expression correlates with metabolic health. Here we generate transgenic mice expressing human Cidea in adipose tissues (aP2-hCidea mice) and show that Cidea is mechanistically associated with a robust increase in adipose tissue expandability. Under humanized conditions (thermoneutrality, mature age and prolonged exposure to high-fat diet), aP2-hCidea mice develop a much more pronounced obesity than their wild-type littermates. Remarkably, the malfunctioning of visceral fat normally caused by massive obesity is fully overcome-perilipin 1 and Akt expression are preserved, tissue degradation is prevented, macrophage accumulation is decreased and adiponectin expression remains high. Importantly, the aP2-hCidea mice display enhanced insulin sensitivity. Our data establish a functional role for Cidea and suggest that, in humans, the association between Cidea levels in white fat and metabolic health is not only correlative but also causative.

G0S2 modulates homeostatic proliferation of naïve CD8⁺ T cells and inhibits oxidative phosphorylation in mitochondria

Since its discovery, diverse functions have been attributed to the G₀/G₁ switch gene 2 (G0S2), from lipid metabolism to control of cell proliferation. Our group showed for the first time that G0S2 promotes quiescence in hematopoietic stem cells by interacting with and retaining nucleolin around the nucleus. Herein, we report the role of G0S2 in the differentiation and function of CD8⁺ T cells examined in mice with an embryonic deletion of the G0s2 gene. G0S2 expression in naïve CD8⁺ T cells decreased immediately after T-cell receptor activation downstream of the MAPK, calcium/calmodulin, PI3K, and mTOR pathways. Surprisingly, G0S2-null naïve CD8⁺ T cells displayed increased basal and spare respiratory capacity that was not associated with increased mitochondrial biogenesis but with increased phosphorylation of AMPKα. Naïve CD8⁺ T cells showed increased proliferation in response to in vitro activation and in vivo lymphopenia; however, naïve CD8⁺ T cells expressing the OT-1 transgene exhibited normal differentiation of naïve cells to effector and memory CD8⁺ T cells upon infection with Listeria monocytogenes in a wild type or a G0s2-null environment, with increased circulating levels of free fatty acids. Collectively, our results suggest that G0S2 inhibits energy production by oxidative phosphorylation to fine-tune proliferation in homeostatic conditions.

Lipolytic inhibitor G0/G1 switch gene 2 inhibits reactive oxygen species production and apoptosis in endothelial cells

G0/G1 switch gene 2 (G0S2), a novel target gene of peroxisome proliferator-activated receptor, is highly expressed in fat tissues. G0S2 acts as proapoptotic factor toward human cancer cells. Endothelial cell (EC) apoptosis may be an initiating event in the development of atherosclerosis. However, the expression and function of G0S2 in vascular ECs remain unknown. Here, we reported for the first time that G0S2 is expressed in arterial ECs. Ectopic expression of G0S2 increased neutral lipid accumulation in cultured ECs. However, G0S2 prevented ECs from serum-free starvation stress- and hydrogen peroxide (H2O2)-induced apoptosis. G0S2 blocked the H2O2-induced dissipation of mitochondrial membrane potential. G0S2 decreased the release of cytochrome c from mitochondria into the cytosol, followed by activation of caspase-9 and caspase-3. The anti-apoptotic effect of G0S2 was Bcl-2 and adipose triglyceride lipase independent. In contrast, gene silence of G0S2 increased serum-free starvation stress-induced EC apoptosis and decreased the formation of capillary-like structures. We further found that G0S2 couples with the F0F1-ATP synthase in ECs. Levels of ATP were elevated, whereas reactive oxygen species levels were reduced in G0S2-expressing ECs. G0S2 can inhibit endothelial denudation secondary to H2O2-induced injury to ECs in vivo. These results indicate that G0S2 acts as a prosurvival molecule in ECs. Taken together, our results indicate that G0S2 has a protective function in ECs and may be a potential target for the treatment of cardiovascular diseases associated with reactive oxygen species-induced EC injury, such as atherosclerosis and restenosis.

Deletion of the gene encoding G0/G 1 switch protein 2 (G0s2) alleviates high-fat-diet-induced weight gain and insulin resistance, and promotes browning of white adipose tissue in mice

AIMS/HYPOTHESIS

Obesity is a global epidemic resulting from increased energy intake, which alters energy homeostasis and results in an imbalance in fat storage and breakdown. G0/G1 switch gene 2 (G0s2) has been recently characterised in vitro as an inhibitor of adipose triglyceride lipase (ATGL), the rate-limiting step in fat catabolism. In the current study we aim to functionally characterise G0s2 within the physiological context of a mouse model.

METHODS

We generated a mouse model in which G0s2 was deleted. The homozygous G0s2 knockout (G0s2 (-/-)) mice were studied over a period of 22 weeks. Metabolic variables were measured including body weight and body composition, food intake, glucose and insulin tolerance tests, energy metabolism and thermogenesis.

RESULTS

We report that G0s2 inhibits ATGL and regulates lipolysis and energy metabolism in vivo. G0s2 (-/-) mice are lean, resistant to weight gain induced by a high-fat diet and are glucose tolerant and insulin sensitive. The white adipose tissue of G0s2 (-/-) mice has enhanced lipase activity and adipocytes showed enhanced stimulated lipolysis. Energy metabolism in the G0s2 (-/-) mice is shifted towards enhanced lipid metabolism and increased thermogenesis. G0s2 (-/-) mice showed enhanced cold tolerance and increased expression of thermoregulatory and oxidation genes within white adipose tissue, suggesting enhanced 'browning' of the white adipose tissue.

CONCLUSIONS/INTERPRETATION

Our data show that G0s2 is a physiological regulator of adiposity and energy metabolism and is a potential target in the treatment of obesity and insulin resistance.

A peptide derived from G0/G1 switch gene 2 acts as noncompetitive inhibitor of adipose triglyceride lipase

The protein G₀/G₁ switch gene 2 (G0S2) is a small basic protein that functions as an endogenous inhibitor of adipose triglyceride lipase (ATGL), a key enzyme in intracellular lipolysis. In this study, we identified a short sequence covering residues Lys-20 to Ala-52 in G0S2 that is still fully capable of inhibiting mouse and human ATGL. We found that a synthetic peptide corresponding to this region inhibits ATGL in a noncompetitive manner in the nanomolar range. This peptide is highly selective for ATGL and does not inhibit other lipases, including hormone-sensitive lipase, monoacylglycerol lipase, lipoprotein lipase, and patatin domain-containing phospholipases 6 and 7. Because increased lipolysis is linked to the development of metabolic disorders, the inhibition of ATGL by G0S2-derived peptides may represent a novel therapeutic tool to modulate lipolysis.

Regulation of fibroblast lipid storage and myofibroblast phenotypes during alveolar septation in mice

Signaling through platelet-derived growth factor receptor-α (PDGFRα) is required for alveolar septation and participates in alveolar regeneration after pneumonectomy. In both adipose tissue and skeletal muscle, bipotent pdgfrα-expressing progenitors expressing delta-like ligand-1 or sex-determining region Y box 9 (Sox9) may differentiate into either lipid storage cells or myofibroblasts. We analyzed markers of mesenchymal progenitors and differentiation in lung fibroblasts (LF) with different levels (absent, low, or high) of pdgfrα gene expression. A larger proportion of pdgfrα-expressing than nonexpressing LF contained Sox9. Neutral lipids, CD166, and Tcf21 were more abundant in LF with a lower compared with a higher level of pdgfrα gene expression. PDGF-A increased Sox9 in primary LF cultures, suggesting that active signaling through PDGFRα is required to maintain Sox9. As alveolar septation progresses from postnatal day (P) 8 to P12, fewer pdgfrα-expressing LF contain Sox9, whereas more of these LF contain myocardin-like transcription factor-A, showing that Sox9 diminishes as LF become myofibroblasts. At P8, neutral lipid droplets predominate in LF with the lower level of pdgfrα gene expression, whereas transgelin (tagln) was predominantly expressed in LF with higher pdgfrα gene expression. Targeted deletion of pdgfrα in LF, which expressed tagln, reduced Sox9 in α-actin (α-SMA, ACTA2)-containing LF, whereas it increased the abundance of cell surface delta-like protein-1 (as well as peroxisome proliferator-activated receptor-γ and tcf21 mRNA in LF, which also expressed stem cell antigen-1). Thus pdgfrα deletion differentially alters delta-like protein-1 and Sox9, suggesting that targeting different downstream pathways in PDGF-A-responsive LF could identify strategies that promote lung regeneration without initiating fibrosis.

Dissecting adipose tissue lipolysis: molecular regulation and implications for metabolic disease

Lipolysis is the process by which triglycerides (TGs) are hydrolyzed to free fatty acids (FFAs) and glycerol. In adipocytes, this is achieved by sequential action of adipose TG lipase (ATGL), hormone-sensitive lipase (HSL), and monoglyceride lipase. The activity in the lipolytic pathway is tightly regulated by hormonal and nutritional factors. Under conditions of negative energy balance such as fasting and exercise, stimulation of lipolysis results in a profound increase in FFA release from adipose tissue (AT). This response is crucial in order to provide the organism with a sufficient supply of substrate for oxidative metabolism. However, failure to efficiently suppress lipolysis when FFA demands are low can have serious metabolic consequences and is believed to be a key mechanism in the development of type 2 diabetes in obesity. As the discovery of ATGL in 2004, substantial progress has been made in the delineation of the remarkable complexity of the regulatory network controlling adipocyte lipolysis. Notably, regulatory mechanisms have been identified on multiple levels of the lipolytic pathway, including gene transcription and translation, post-translational modifications, intracellular localization, protein-protein interactions, and protein stability/degradation. Here, we provide an overview of the recent advances in the field of AT lipolysis with particular focus on the molecular regulation of the two main lipases, ATGL and HSL, and the intracellular and extracellular signals affecting their activity.