Adipose Triglyceride Lipase Activity Research Articles

Sirtuin 1 Inhibits Fatty Acid Synthesis through Forkhead Box Protein O1-Mediated Adipose Triglyceride Lipase Expression in Goat Mammary Epithelial Cells

Sirtuin 1 (SIRT1) is a key upstream regulator of lipid metabolism; however, the molecular mechanisms by which SIRT1 regulates milk fat synthesis in dairy goats remain unclear. This study aimed to investigate the regulatory roles of SIRT1 in modulating lipid metabolism in goat mammary epithelial cells (GMECs) and its impact on the adipose triglyceride lipase (ATGL) promoter activity using RNA interference (RNAi) and gene overexpression techniques. The results showed that SIRT1 is significantly upregulated during lactation compared to the dry period. Additionally, SIRT1 knockdown notably increased the expressions of genes related to fatty acid synthesis (SREBP1, SCD1, FASN, ELOVL6), triacylglycerol (TAG) production (DGAT2, AGPAT6), and lipid droplet formation (PLIN2). Consistent with the transcriptional changes, SIRT1 knockdown significantly increased the intracellular contents of TAG and cholesterol and the lipid droplet abundance in the GMECs, while SIRT1 overexpression had the opposite effects. Furthermore, the co-overexpression of SIRT1 and Forkhead box protein O1 (FOXO1) led to a more pronounced increase in ATGL promoter activity, and the ability of SIRT1 to enhance ATGL promoter activity was nearly abolished when the FOXO1 binding sites (FKH1 and FKH2) were mutated, indicating that SIRT1 enhances the transcriptional activity of ATGL via the FKH element in the ATGL promoter. Collectively, our data reveal that SIRT1 enhances the transcriptional activity of ATGL through the FOXO1 binding sites located in the ATGL promoter, thereby regulating lipid metabolism. These findings provide novel insights into the role of SIRT1 in fatty acid metabolism in dairy goats.

Dietary manganese supplementation decreases hepatic lipid deposition by regulating gene expression and enzyme activity involved in lipid metabolism in the liver of broilers.

This study aimed to characterize the effects of different dietary forms of supplemental manganese (Mn) on hepatic lipid deposition, gene expression, and enzyme activity in liver fat metabolism in 42-d-old broiler chickens. In total 420 one-day-old Arbor Acres (AA) broilers (rooster:hen = 1:1) were assigned randomly based on body weight and sex to 1 of 6 treatments (10 replicate cages per treatment and 7 broilers per replicate cage) in a completely randomized design using a 2 (sex) × 3 (diet) factorial arrangement. The 3 diets were basal control diets without Mn supplementation and basal diets supplemented with either Mn sulfate or Mn proteinate. No sex × diet interactions were observed in any of the measured indexes; thus, the effect of diet alone was presented in this study. Dietary Mn supplementation increased Mn content in the plasma and liver, adipose triglyceride lipase (ATGL) activity, and ATGL mRNA and its protein expression in the liver by 5.3% to 24.0% (P < 0.05), but reduced plasma triglyceride (TG), total cholesterol, and low-density lipoprotein (LDL-C) levels, liver TG content, fatty acid synthase (FAS) and malic enzyme (ME) activities, mRNA expression of sterol-regulatory element-binding protein 1 (SREBP1), FAS, stearoyl-coA desaturase (SCD), and ME, as well as the protein expression of SREBP1 and SCD in the liver by 5.5% to 22.8% (P < 0.05). No differences were observed between the 2 Mn sources in all of the determined parameters. Therefore, it was concluded that dietary Mn supplementation, regardless of Mn source, decreased hepatic lipid accumulation in broilers by inhibiting SREBP1 and SCD expression, FAS and ME activities, and enhancing ATGL expression and activity.

Coix Sprouts Affect Triglyceride Metabolism in Huh7 Cells and High-Fat Diet-Induced Obese Mice.

Lipolysis is the hydrolysis of triglycerides (TGs), commonly known as fats. Intracellular lipolysis of TG is associated with adipose triglyceride lipase (ATGL), which provides fatty acids during times of metabolic need. The aim of this study was to determine whether Coix lacryma-jobi L. var. ma-yuen Stapf (Coix) sprouts (CS) can alleviate obesity through lipolysis. Overall, we investigated the potential of CS under in vitro and invivo conditions and confirmed the underlying mechanisms. Huh7 cells were exposed to free fatty acids (FFAs), and C57BL/6J mice were fed a 60% high-fat diet. When FFA were introduced into Huh7 cells, the intracellular TG levels increased within the Huh7 cells. However, CS treatment significantly reduced intracellular TG levels. Furthermore, CS decreased the expression of Pparγ and Srebp1c mRNA and downregulated the mutant Pnpla3 (I148M) mRNA. Notably, CS significantly upregulated ATGL expression. CS treatment at a dose of 200 mg/kg/day resulted in a significant and dose-dependent decrease in body weight gain and epididymal adipose tissue weight. Specifically, the group treated with CS (200 mg/kg/day) exhibited a significant modulation of serum lipid biomarkers. In addition, CS ameliorated histological alterations in both the liver and adipose tissues. In summary, CS efficiently inhibited lipid accumulation through the activation of the lipolytic enzyme ATGL coupled with the suppression of enzymes involved in TG synthesis. Consequently, CS show promise as a potential anti-obesity agent.

Discovery and Development of Quinazolinones and Quinazolinediones for Ameliorating Nonalcoholic Fatty Liver Disease (NAFLD) by Modulating COP1-ATGL Axis.

E3 ubiquitin ligase, Constitutive Photomorphogenic 1 (COP1) regulates turnover of Adipose Triglyceride Lipase (ATGL), the rate-limiting lipolytic enzyme. Genetic perturbation in the COP1-ATGL axis disrupts lipid homeostasis, leading to liver steatosis. Using drug development strategies, we herein report quinazolinone and quinazolinedione based modulators for COP1-ATGL axis. Systematic SAR studies and subsequent optimization were performed by incorporating relevant functional groups at the N1, N3, C5, and C6 positions of both scaffolds. Compounds' efficacy was evaluated by multiple biological assays and ADME profiling. The lead compound 86 could increase ATGL protein expression, reduce ATGL ubiquitination and COP1 autoubiquitination, and diminish lipid accumulation in hepatocytes in the nanomolar range. Oral administration of 86 abrogated triglyceride accumulation and resolved fibrosis in preclinical Nonalcoholic Fatty Liver Disease (NAFLD) model. The study thus establishes quinazolinedione as a viable chemotype to therapeutically modulate the activity of COP1 and ATGL in relevant clinical contexts.

Effect of dietary manganese supplementation on abdominal fat deposition of broilers1

Excessive abdominal fat deposition seriously restricts the production efficiency of broilers. Several studies found that dietary supplemental manganese (Mn) could effectively reduce the abdominal fat deposition of broilers, but the underlying mechanisms remain unclear. The present study aimed to investigate the effect of dietary supplementation with the inorganic or organic Mn on abdominal fat deposition, and enzyme activity and gene expression involved in lipid metabolism in the abdominal fat of male or female broilers. A total of 420 1-d-old AA broilers (half males and half females) were randomly allotted by body weight and gender to 1 of 6 treatments with 10 replicate cages of 7 chicks per cage in a completely randomized design involving a 3 (dietary Mn addition)×2 (gender) factorial arrangement. Male or female broilers were fed with the Mn-unsupplemented basal diets containing 17.52 mg Mn kg-1 (d 1-21) and 15.62 mg Mn kg-1 (d 22-42) by analysis or the basal diets supplemented with 110 mg Mn kg-1 (d 1-21) and 80 mg Mn kg-1 (d 22-42) as either the Mn sulfate or the Mn proteinate with moderate chelation strength (Mn-Prot M) for 42 d. The results showed that the interaction between dietary Mn addition and gender had no impact (P>0.05) on any of the measured parameters; abdominal fat percentage of broilers was decreased (P<0.003) by Mn addition; Mn addition increased (P<0.004) adipose triglyceride lipase (ATGL) activity, while Mn-Prot M decreased (P<0.002) the fatty acid synthase (FAS) activity in the abdominal fat of broilers compared to the control; Mn addition decreased (P<0.009) diacylglycerol acyltransferase 2 (DGAT2) mRNA expression level and peroxisome proliferator-activated receptor γ (PPARγ) mRNA and protein expression levels, but up-regulated (P<0.05) the ATGL mRNA and protein expression levels in the abdominal fat of broilers. It was concluded that dietary supplementation with Mn inhibited the abdominal fat deposition of broilers possibly via decreasing the expression of PPARγ and DGAT2 as well as increasing the expression and activity of ATGL in the abdominal fat of broilers, and Mn-Prot M was more effective in inhibiting the FAS acitivity.

Effect of Cold Exposure and Exercise on Insulin Sensitivity and Serum Free Fatty Acids in Obese Rats.

This study aimed to explore the effect of exercise and cold exposure on insulin sensitivity and the level of serum free fatty acids (FFA) in diet-induced obese rats. Sixty-four diet-induced obese rats were randomly assigned to eight groups: room temperature-sedentary, room temperature-exercise, acute cold exposure-sedentary, acute cold exposure-exercise, intermittent cold exposure-sedentary, intermittent cold exposure-exercise, sustained cold exposure-sedentary, and sustained cold exposure-exercise. After the interventions, the homeostatic model assessment for insulin resistance (HOMA-IR) values, the level of serum FFA, subcutaneous fat ratio (SFR) and visceral fat ratio, enzyme activities of adipose triglyceride lipase, and lipoprotein lipase (LPL) in inguinal adipose tissue, and protein expression of PGC1-α and p38 MAPK in skeletal muscle were investigated. We found that exercise ( P = 0.0136) and cold exposure ( P < 0.0001) reduced HOMA-IR values independently. Exercise reduced serum FFA ( P = 0.0041), whereas cold exposure did not affect them. Moreover, the HOMA-IR values were positively correlated with the serum FFA levels ( r = 0.32, P = 0.01). SFR or visceral fat ratio was coordinately reduced by the interaction (for SFR, P = 0.0015) or opposing main effects between or of cold exposure and exercise, supporting the reduction of serum FFA. However, cold exposure or exercise increased the activity of adipose triglyceride lipase and LPL independently or interactively (for LPL, P = 0.0143), suggesting an increase in serum FFA. Finally, cold exposure and exercise enhanced protein expression of PGC1-α and p38 MAPK independently or interactively (for p38 MAPK, P = 0.0226), suggesting increased uptake and oxidation of serum FFA in muscle. These results suggest that the combination of exercise and cold exposure may result in more serum FFA utilization than production and thus lead to reduced serum FFA and increased insulin sensitivity.

The FoxO1-ATGL axis alters milk lipolysis homeostasis through PI3K/AKT signaling pathway in dairy goat mammary epithelial cells.

Goat milk is enriched in fatty acids which are beneficial to human health. Previous research has revealed that 98% of milk fat is composed of triglycerides. However, the mechanisms regulating milk fat composition remain unclear. Forkhead box protein O1 (FoxO1) is a crucial regulatory factor involved in lipid metabolism across various cell types. Chromatin immunoprecipitation sequencing (ChIP)-seq data) and RNA sequencing (RNA-seq) data revealed that have indicated a close association between FoxO1 was closely related to lipid metabolism during lactation in dairy goats. The objective of this study was to investigate the mechanisms by which FoxO1 regulates lipid metabolism in goat mammary epithelial cells (GMECs). FoxO1 knockdown significantly downregulated the expression of adipose triglyceride lipase (ATGL) and suppressed the activity of the ATGL promoter. Consistently, the number of lipid droplets decreased significantly in FoxO1-overexpressing cells and increased in ATGL-knockdown cells. To further verify the effect of FoxO1 on ATGL promoter activity, cells were transfected with four promoter fragments of different lengths. We found that the core region of the ATGL promoter was located between -882 bp and -524 bp, encompassing two FoxO1 binding sites (FKH1 and FKH2). Mutations in the FoxO1 binding sites significantly downregulated ATGL promoter activity in GMECs. Luciferase reporter assays demonstrated that FoxO1 overexpression markedly enhanced ATGL promoter activity. Furthermore, site-directed mutation confirmed that FKH1 and FKH2 sites were simultaneously mutated significantly attenuated the stimulatory effect of FoxO1 on ATGL promoter activities simultaneous mutation of FKH1 and FKH2 sites significantly attenuated the stimulatory effect of FoxO1 on ATGL promoter activity. ChIP assays showed that FoxO1 directly binds to the FKH2 element located in the ATGL promoter in vivo. Finally, immunofluorescence staining revealed that insulin promotes the translocation of FoxO1 from the nucleus to the cytoplasm, thereby attenuating the FoxO1-induced activation of the ATGL promoter. Collectively, these findings uncover a novel pathway where by FoxO1 may regulate lipid metabolism in GMECs specifically by modulating the transcriptional activity of ATGL.

PNPLA3(I148M) Inhibits Lipolysis by Perilipin-5-Dependent Competition with ATGL.

The single nucleotide polymorphism I148M of the lipase patatin-like phospholipase domain containing 3 (PNPLA3) is associated with an unfavorable prognosis in alcoholic and non-alcoholic steatohepatitis (ASH, NASH), with progression to liver cirrhosis and development of hepatocellular carcinoma. In this study, we investigated the mechanistic interaction of PNPLA3 with lipid droplet (LD)-associated proteins of the perilipin family, which serve as gatekeepers for LD degradation. In a collective of 106 NASH, ASH and control liver samples, immunohistochemical analyses revealed increased ballooning, inflammation and fibrosis, as well as an accumulation of PNPLA3-perilipin 5 complexes on larger LDs in patients homo- and heterozygous for PNPLA3(I148M). Co-immunoprecipitation demonstrated an interaction of PNPLA3 with perilipin 5 and the key enzyme of lipolysis, adipose triglyceride lipase (ATGL). Localization studies in cell cultures and human liver showed colocalization of perilipin 5, ATGL and PNPLA3. Moreover, the lipolytic activity of ATGL was negatively regulated by PNPLA3 and perilipin 5, whereas perilipin 1 displaced PNPLA3 from the ATGL complex. Furthermore, ballooned hepatocytes, the hallmark of steatohepatitis, were positive for PNPLA3 and perilipins 2 and 5, but showed decreased perilipin 1 expression with respect to neighboured hepatocytes. In summary, PNPLA3- and ATGL-driven lipolysis is significantly regulated by perilipin 1 and 5 in steatohepatitis.

Microsomal triglyceride transfer protein regulates intracellular lipolysis in adipocytes independent of its lipid transfer activity

BackgroundThe triglyceride (TG) transfer activity of microsomal triglyceride transfer protein (MTP) is essential for lipoprotein assembly in the liver and intestine; however, its function in adipose tissue, which does not assemble lipoproteins, is unknown. Here we have elucidated the function of MTP in adipocytes. Approach and resultsWe demonstrated that MTP is present on lipid droplets in human adipocytes. Adipose-specific MTP deficient (A-Mttp−/−) male and female mice fed an obesogenic diet gained less weight than Mttpf/f mice, had less fat mass, smaller adipocytes and were insulin sensitive. A-Mttp−/− mice showed higher energy expenditure than Mttpf/f mice. During a cold challenge, A-Mttp−/− mice maintained higher body temperature by mobilizing more fatty acids. Biochemical studies indicated that MTP deficiency de-repressed adipose triglyceride lipase (ATGL) activity and increased TG lipolysis. Both wild type MTP and mutant MTP deficient in TG transfer activity interacted with and inhibited ATGL activity. Thus, the TG transfer activity of MTP is not required for ATGL inhibition. C-terminally truncated ATGL that retains its lipase activity interacted less efficiently than full-length ATGL. ConclusionOur findings demonstrate that adipose-specific MTP deficiency increases ATGL-mediated TG lipolysis and enhances energy expenditure, thereby resisting diet-induced obesity. We speculate that the regulatory function of MTP involving protein-protein interactions might have evolved before the acquisition of TG transfer activity in vertebrates. Adipose-specific inhibition of MTP-ATGL interactions may ameliorate obesity while avoiding the adverse effects associated with inhibition of the lipid transfer activity of MTP.

Human CIDEC transgene improves lipid metabolism and protects against high-fat diet–induced glucose intolerance in mice

Cell death–inducing DNA fragmentation factor-like effector C (CIDEC) expression in adipose tissue positively correlates with insulin sensitivity in obese humans. Further, E186X, a single-nucleotide CIDEC variant is associated with lipodystrophy, hypertriglyceridemia, and insulin resistance. To establish the unknown mechanistic link between CIDEC and maintenance of systemic glucose homeostasis, we generated transgenic mouse models expressing CIDEC (Ad-CIDECtg) and CIDEC E186X variant (Ad-CIDECmut) transgene specifically in the adipose tissue. We found that Ad-CIDECtg but not Ad-CIDECmut mice were protected against high-fat diet-induced glucose intolerance. Furthermore, we revealed the role of CIDEC in lipid metabolism using transcriptomics and lipidomics. Serum triglycerides, cholesterol, and low-density lipoproteins were lower in high-fat diet-fed Ad-CIDECtg mice compared to their littermate controls. Mechanistically, we demonstrated that CIDEC regulates the enzymatic activity of adipose triglyceride lipase via interacting with its activator, CGI-58, to reduce free fatty acid release and lipotoxicity. In addition, we confirmed that CIDEC is indeed a vital regulator of lipolysis in adipose tissue of obese humans, and treatment with recombinant CIDEC decreased triglyceride breakdown in visceral human adipose tissue. Our study unravels a central pathway whereby adipocyte-specific CIDEC plays a pivotal role in regulating adipose lipid metabolism and whole-body glucose homeostasis. In summary, our findings identify human CIDEC as a potential ‘drug’ or a ‘druggable’ target to reverse obesity-induced lipotoxicity and glucose intolerance.

Molecular Modeling of ABHD5 Structure and Ligand Recognition.

Alpha/beta hydrolase domain-containing 5 (ABHD5), also termed CGI-58, is the key upstream activator of adipose triglyceride lipase (ATGL), which plays an essential role in lipid metabolism and energy storage. Mutations in ABHD5 disrupt lipolysis and are known to cause the Chanarin-Dorfman syndrome. Despite its importance, the structure of ABHD5 remains unknown. In this work, we combine computational and experimental methods to build a 3D structure of ABHD5. Multiple comparative and machine learning-based homology modeling methods are used to obtain possible models of ABHD5. The results from Gaussian accelerated molecular dynamics and experimental data of the apo models and their mutants are used to select the most likely model. Moreover, ensemble docking is performed on representative conformations of ABHD5 to reveal the binding mechanism of ABHD5 and a series of synthetic ligands. Our study suggests that the ABHD5 models created by deep learning-based methods are the best candidate structures for the ABHD5 protein. The mutations of E41, R116, and G328 disturb the hydrogen bonding network with nearby residues and suppress membrane targeting or ATGL activation. The simulations also reveal that the hydrophobic interactions are responsible for binding sulfonyl piperazine ligands to ABHD5. Our work provides fundamental insight into the structure of ABHD5 and its ligand-binding mode, which can be further applied to develop ABHD5 as a therapeutic target for metabolic disease and cancer.

Molecular Basis for Membrane Binding and Lipolysis Activation by ABHD5

Triglycerides are the main reservoir for long‐term energy storage in humans and are stored intracellularly in lipid droplets. Abnormal triglyceride metabolism is a key factor leading to obesity, diabetes, fatty liver disease and cardiovascular disease. When energy is needed, triglycerides are broken down in a metabolic pathway called lipolysis. Intracellular lipolysis is initiated by adipose triglyceride lipase (ATGL), which hydrolyzes triacylglycerol (TAG) to make diacylglycerol and a free fatty acid. Alpha‐beta hydrolase domain‐containing 5 (ABHD5) is a highly conserved regulator of ATGL‐mediated lipolysis that increases ATGL activity and is necessary to maintain lipid homeostasis. Consistently, mutations in ABHD5 cause Chanarin‐Dorfman syndrome, which leads to excessive accumulation of triglycerides. Despite over two decades of studies using biochemical approaches to mouse models, the structure of ABHD5 and molecular mechanisms of regulation remained uncharacterized. To understand the mechanism, we purified full‐length human ABHD5, visualized its self‐assembled, multiple oligomeric state in the absence of detergents by cryo‐EM, and generated preliminary crystals of detergent‐solubilized, monomeric ABHD5. We found ABHD5 is phosphorylated in vitro by PKA and recruited to membranes by specific lipids. We also purified the full‐length human ATGL. To further investigate the structural and regulation mechanisms of ABHD5 and ATGL, we will utilize hydrogen deuterium exchange mass spectrometry to map ATGL and ABHD5 protein‐protein and protein‐membrane interactions, biochemical experiments to study their co‐activation mechanism and membrane interaction. This study will provide a deeper understanding for the clinically relevant mutations, membrane recruitment and lipolysis activation of these key players in lipid metabolism.

Plin5 Bidirectionally Regulates Lipid Metabolism in Oxidative Tissues.

Cytoplasmic lipid droplets (LDs) can store neutral lipids as an energy source when needed and also regulate the key metabolic processes of intracellular lipid accumulation, which is associated with several metabolic diseases. The perilipins (Plins) are a family of proteins that associate with the surface of LDs. As a member of Plins superfamily, perilipin 5 (Plin5) coats LDs in cardiomyocytes, which is significantly related to reactive oxygen species (ROS) production originated from mitochondria in the heart, consequently determining the progression of diabetic cardiomyopathy. Plin5 may play a bidirectional function in lipid metabolism which is in a state of dynamic balance. In the basic state, Plin5 inhibited the binding of comparative gene identification-58 (CGI-58) to adipose triglyceride lipase (ATGL) by binding CGI-58, thus inhibiting lipolysis. However, when the body is under stress (such as cold, fasting, exercise, and other stimuli), protein kinase A (PKA) phosphorylates and activates Plin5, which then causes Plin5 to release the binding site of CGI-58 and ATGL, prompting CGI-58 to bind to ATGL and activate ATGL activity, thus accelerating the lipolysis process, revealing the indispensable role of Plin5 in lipid turnover. Here, the purpose of this review is to summarize the present understanding of the bidirectional regulation role of Plin5 in oxidative tissues and to reveal its potential role in diabetic cardiomyopathy protection.

Farnesoid X receptor (FXR) and G protein-coupled bile acid receptor 1 (TGR5) signaling pathways improved the hepatic lipid metabolism in hybrid grouper

In the present study, juvenile hybrid grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂) were intraperitoneally injected with taurocholic acid (I-TCA), obeticholic acid (FXR agonist, I-T747), guggulsterone (FXR antagonist, I-TGU), SBI-115 (TGR5 antagonist, I-TSBI), and INT-777 (TGR5 agonist, I-T777), respectively. The results showed that the fish injected with 50 mg kg−1 TCA three times during a 144 h period exhibited significantly lower hepatic lipid accumulation, compared to other concentrations and periods. Compared to the I-TCA group, the I-T747 treatment significantly increased the activities of hepatic adipose triglyceride lipase (ATGL) and carnitine palmitoyltransferase 1 (CPT1), as well as the expression of lipolysis and fatty acid uptake genes, while significantly decreased the conten of hepatic crude lipid, the activity of CPT1, and the expression of lipogenesis genes. Meanwhile, the I-TGU treatment significantly increased hepatic lipid deposition and the expression of lipogenesis genes. Compared to the I-TCA group, the I-T777 treatment did not significantly affect the parameters related to lipid deposition, but it significantly decreased the activities of acetyl-CoA carboxylase (ACC), CPT1, and fatty acid synthase (FAS), while significantly increasing the activity of ATGL and the expression of lipolysis and fatty acid uptake-related genes. Meanwhile, the I-TSBI treatment significantly increased the hepatic lipid accumulation, the activities of ACC, CPT1 and FAS, and the expression of lipogenesis and lipogenic transcriptional factors genes. In conclusion, activation of the FXR protected against the hepatic lipid accumulation by enhancing the lipolysis, while inhibition of FXR or TGR5 induced the hepatic lipid accumulation by enhancing the lipogenesis in hybrid grouper.

Lipopolysaccharide induces lipolysis and insulin resistance in adipose tissue from dairy cows

Intense and protracted adipose tissue (AT) fat mobilization increases the risk of metabolic and inflammatory periparturient diseases in dairy cows. This vulnerability increases when cows have endotoxemia-common during periparturient diseases such as mastitis, metritis, and pneumonia-but the mechanisms are unknown. Fat mobilization intensity is determined by the balance between lipolysis and lipogenesis. Around parturition, the rate of lipolysis surpasses that of lipogenesis, leading to enhanced free fatty acid release into the circulation. We hypothesized that exposure to endotoxin (ET) increases AT lipolysis by activation of classic and inflammatory lipolytic pathways and reduction of insulin sensitivity. In experiment 1, subcutaneous AT (SCAT) explants were collected from periparturient (n = 12) Holstein cows at 11 ± 3.6 d (mean ± SE) before calving, and 6 ± 1 d and 13 ± 1.4 d after parturition. Explants were treated with the endotoxin lipopolysaccharide (LPS; 20 µg/mL; basal = 0 µg/mL) for 3 h. The effect of LPS on lipolysis was assessed in the presence of the β-adrenergic agonist and promoter of lipolysis isoproterenol (ISO; 1 µM; LPS+ISO). In experiment 2, SCAT explants were harvested from 24 nonlactating, nongestating multiparous Holstein dairy cows and exposed to the same treatments as in experiment 1 for 3 and 7 h. The effect of LPS on the antilipolytic responses induced by insulin (INS = 1 µL/L, LPS+INS) was established during ISO stimulation [ISO+INS, LPS+ISO+INS]. The characterization of lipolysis included the quantification of glycerol release and the assessment of markers of lipase activity [adipose triglyceride lipase (ATGL), hormone-sensitive lipase (HSL), and phosphorylated HSL Ser563 (pHSL)], and insulin pathway activation (AKT, pAKT) using capillary electrophoresis. Inflammatory gene networks were evaluated by real-time quantitative PCR. In periparturient cows, LPS increased AT lipolysis by 67 ± 12% at 3 h across all time points compared with basal. In nonlactating cows, LPS was an effective lipolytic agent at 3 h and 7 h, increasing glycerol release by 115 ± 18% and 68.7 ± 16%, respectively, relative to basal. In experiment 2, LPS enhanced ATGL activity with minimal HSL activation at 3 h. In contrast, at 7 h, LPS increased HSL phosphorylation (i.e., HSL activity) by 123 ± 11%. The LPS-induced HSL lipolytic activity at 7 h coincided with the activation of the MEK/ERK inflammatory pathway. In experiment 2, INS reduced the lipolytic effect of ISO (ISO+INS: -63 ± 18%) and LPS (LPS+INS: -45.2 ± 18%) at 3 h. However, the antilipolytic effect of INS was lost in the presence of LPS at 7 h (LPS+INS: -16.3 ± 16%) and LPS+ISO+INS at 3 and 7 h (-3.84 ± 23.6% and -21.2 ± 14.6%). Accordingly, LPS reduced pAKT:AKT (0.11 ± 0.07) compared with basal (0.18 ± 0.05) at 7 h. Our results indicated that exposure to LPS activated the classic and inflammatory lipolytic pathways and reduced insulin sensitivity in SCAT. These data provide evidence that during endotoxemia, dairy cows may be more susceptible to lipolysis dysregulation and loss of adipocyte sensitivity to the antilipolytic action of insulin.

Biophysical characterization and a roadmap towards the NMR solution structure of G0S2, a key enzyme in non-alcoholic fatty liver disease.

In the United States non-alcoholic fatty liver disease (NAFLD) is the most common form of chronic liver disease, affecting an estimated 80 to 100 million people. It occurs in every age group, but predominantly in people with risk factors such as obesity and type 2 diabetes. NAFLD is marked by fat accumulation in the liver leading to liver inflammation, which may lead to scarring and irreversible damage progressing to cirrhosis and liver failure. In animal models, genetic ablation of the protein G0S2 leads to alleviation of liver damage and insulin resistance in high fat diets. The research presented in this paper aims to aid in rational based drug design for the treatment of NAFLD by providing a pathway for a solution state NMR structure of G0S2. Here we describe the expression of G0S2 in an E. coli system from two different constructs, both of which are confirmed to be functionally active based on the ability to inhibit the activity of Adipose Triglyceride Lipase. In one of the constructs, preliminary NMR spectroscopy measurements show dominant alpha-helical characteristics as well as resonance assignments on the N-terminus of G0S2, allowing for further NMR work with this protein. Additionally, the characterization of G0S2 oligomers are outlined for both constructs, suggesting that G0S2 may defensively exist in a multimeric state to protect and potentially stabilize the small 104 amino acid protein within the cell. This information presented on the structure of G0S2 will further guide future development in the therapy for NAFLD.

SIRT5 Inhibition Induces Brown Fat-Like Phenotype in 3T3-L1 Preadipocytes.

Brown adipose tissue (BAT) activity plays a key role in regulating systemic energy. The activation of BAT results in increased energy expenditure, making this tissue an attractive pharmacological target for therapies against obesity and type 2 diabetes. Sirtuin 5 (SIRT5) affects BAT function by regulating adipogenic transcription factor expression and mitochondrial respiration. We analyzed the expression of SIRT5 in the different adipose depots of mice. We treated 3T3-L1 preadipocytes and mouse primary preadipocyte cultures with the SIRT5 inhibitor MC3482 and investigated the effects of this compound on adipose differentiation and function. The administration of MC3482 during the early stages of differentiation promoted the expression of brown adipocyte and mitochondrial biogenesis markers. Upon treatment with MC3482, 3T3-L1 adipocytes showed an increased activation of the AMP-activated protein kinase (AMPK), which is known to stimulate brown adipocyte differentiation. This effect was paralleled by an increase in autophagic/mitophagic flux and a reduction in lipid droplet size, mediated by a higher lipolytic rate. Of note, MC3482 increased the expression and the activity of adipose triglyceride lipase, without modulating hormone-sensitive lipase. Our findings reveal that SIRT5 inhibition stimulates brown adipogenesis in vitro, supporting this approach as a strategy to stimulate BAT and counteract obesity.

Distinct roles of adipose triglyceride lipase and hormone‐sensitive lipase in the catabolism of triacylglycerol estolides

Branched esters of fatty acids and hydroxy fatty acids (FAHFAs) belong to a wide range group of lipids, some of which have anti-inflammatory and anti-diabetic properties. FAHFAs themselves belong to oligomeric FA esters, known as estolides. Depending on structure, they are divided in subfamilies (e.g. palmitic acid esters of hydroxy stearic acid, PAHSAs) including several regioisomers with different position of the branching position (e.g. 9-PAHSA). In human and mice tissue, glycerol-bound FAHFAs in triacylglycerols (TAGs), named TAG estolides, serve as metabolite reservoir of FAHFAs mobilized by lipases upon demand. Here, we studied the role of two major metabolic lipases, adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL), in TAG estolide and FAHFA degradation. We synthesized a panel of twenty TAG estolide isomers with different FAHFAs groups varying in branching position, chain length, saturation grade, and position on the glycerol backbone. An in silico mass spectra library was developed of all predicted catabolic intermediates. Homogenates of HEK293T cells overexpressing ATGL, or HSL were used for the determination of TAG estolide hydrolase activity of HSL and ATGL in the presence or absence of comparative gene identification-58 (CGI-58). White adipose tissue from ad libitum fed and fasted wild-type and global HSL knock-out mice was collected and TAG estolides were quantified. We found that ATGL alone or coactivated by CGI-58 efficiently liberated FAHFAs from TAG estolides with a preference for more compact substrates where the estolide branching point is located near the glycerol ester bond. ATGL also participated in transesterification and remodeling reactions leading to the formation of TAG estolides with alternative acyl compositions. HSL represented a much more potent estolide bond hydrolase for both TAG estolides and free FAHFAs. FAHFA and TAG estolide accumulation in white adipose tissue of mice lacking HSL argued for a functional role of HSL in estolide catabolism in vivo. Our data show that ATGL and HSL participate in the metabolism of estolides and TAG estolides in distinct manners and are likely to affect the lipokine function of FAHFAs.

ROS-dependent HIF1\u03b1 activation under forced lipid catabolism entails glycolysis and mitophagy as mediators of higher proliferation rate in cervical cancer cells

BackgroundIn the last decades, the concept of metabolic rewiring as a cancer hallmark has been expanded beyond the “Warburg effect” and the importance of other metabolic routes, including lipid metabolism, has emerged. In cancer, lipids are not only a source of energy but are also required for the formation of membranes building blocks, signaling and post-translational modification of proteins. Since lipid metabolism contributes to the malignancy of cancer cells, it is an attractive target for therapeutic strategies.MethodsOver-expression of the adipose triglyceride lipase (ATGL) was used to boost lipid catabolism in cervical cancer cells. The cervical cancer cell line HeLa was employed as the primary experimental model for all subsequent studies. The lipolytic activity of ATGL was mimicked by caproate, a short-chain fatty acid that is efficiently oxidized in mitochondria.ResultsHere, we provide evidence of the association between boosted lipid catabolism and the increased proliferation and migration capability of cervical cancer cells. These pro-tumoral effects were ascribed to the reactive oxygen species (ROS)-mediated induction of hypoxia-inducible factor-1α (HIF1α) triggered by the increased mitochondrial fatty acids (FAs) oxidation. HIF1α activation increases glycolytic flux and lactate production, promoting cell proliferation. At the same time, HIF1α increases protein and mRNA levels of its known target BCL2 and adenovirus E1B 19-kDa-interacting protein 3 (BNIP3), which in turn activates mitophagy as a pro-survival process, as demonstrated by the induction of apoptosis upon inhibition of mitophagy. These effects were mimicked by the short-chain fatty acid caproate, confirming that forcing lipid catabolism results in HIF1α induction.ConclusionsBoosting lipid catabolism by ATGL over-expression has a pro-tumor role in cervical cancer cells, dependent on ROS production and HIF1α induction. Together with the bioinformatics evidence of the correlation of ATGL activity with the aggressiveness of cervical cancer cells, our data suggest that ATGL could be a promising prognostic marker for cervical cancer and highlight the need of further investigations on the role of this lipase in cancer cells. This evidence could be exploited to develop new personalized therapy, based on the functionality of the antioxidant equipment of cancer cells, considering that ROS content could affect ATGL role.

Single-cell RNA sequencing of preadipocytes reveals the cell fate heterogeneity induced by melatonin.

Obesity is a global epidemic health disorder and associated with several diseases. Body weight-reducing effects of melatonin have been reported; however, no investigation toward examining whether the beneficial effects of melatonin are associated with preadipocyte heterogeneity has been reported. In this study, we profiled 25071 transcriptomes of normal and melatonin-treated preadipocytes using scRNA-seq. By tSNE analysis, we present a cellular-state landscape for melatonin-treated preadipocytes that covers multiple-cell subpopulations, defined as cluster 0 to cluster 13. Cluster 0 and cluster 1 were the largest components of normal and melatonin-treated preadipocytes, respectively. G0S2, an inhibitor of adipose triglyceride lipase (ATGL), was significantly upregulated in cluster 0 and downregulated in cluster 1. We redefined cluster 0 as the G0S2-positive cluster (G0S2+ ) and cluster 1 as the G0S2-negative cluster (G0S2- ). Through pseudotime analysis, the G0S2- cluster cell differentiation trajectory was divided into three major structures, that is, the prebranch, the lipid catabolism branch, and the cell fate 2 branch. In vitro, G0S2 knockdown enhanced the expression levels of ATGL, BAT markers and fatty acid oxidation-related genes, but inhibited C/EBPα and PPARγ expression. In vivo, knockdown of G0S2 reduced the body weight gain in high-fat-fed mice. The beneficial effects of the G0S2- cell cluster in promoting lipolysis and inhibiting adipogenesis are dependent on two major aspects: first, downregulation of the G0S2 gene in the G0S2- cluster, resulting in activation of ATGL, which is responsible for the bulk of triacylglycerol hydrolase activity; and second, upregulation of FABP4 in the G0S2- cluster, resulting in inhibition of PPARγ and further reducing adipogenesis.