Cardiohistological Findings in Refeeding Syndrome.

Severe eating disorders may develop refeeding syndrome, which sometimes resembles severe cardiac dysfunction. A woman in her thirties was admitted to our hospital because of cardiogenic shock. Transthoracic echocardiography showed reduced left ventricular systolic function. In her medical history, she had been diagnosed with refeeding syndrome. A ventricular endocardial biopsy was performed to exclude other cardiac diseases. A histological examination showed conspicuously atrophied cardiomyocytes with nuclear swelling and irregularities; the myocardial sequence was disturbed with fibrosis. Immunostaining revealed that lipid droplet markers, adipose triglyceride lipase, and perilipin 2 were poorly observed in the cardiomyocytes, while expression of both proteins was attenuated in fibroblasts within the myocardial layer. The abnormal metabolism of fatty acids was the presumed cause of cardiac dysfunction.

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.

Dilated cardiomyopathy caused by mutation of the PNPLA2 gene: a case report and literature review.

Deficiency of adipose triglyceride lipase (ATGL) due to mutation in PNPLA2 causes neutral lipid storage disease with myopathy (NLSDM), an autosomal recessive disorder (MIM: #610717). NLSDM patients are mainly affected by progressive myopathy, cardiomyopathy, and hepatomegaly. Cardiac involvement was reported in 40%-50% of NLSDM patients. Patients with cardiac involvement have adult-onset progressive heart failure, mimicking dilated or hypertrophic cardiomyopathy. The clinical characteristics, genotype-phenotype correlation, and prognosis of cardiomyopathy secondary to PNPLA2 mutation are not understood. We reported two male patients carrying a homozygous splicing mutation NM_020376.4 (c.757 + 1G>T) in PNPLA2, presenting with severe dilated cardiomyopathy and mild skeletal muscle involvement. Through the literature review, the ECG and imaging features and the prognosis of 49 previously reported cases of cardiomyopathy caused by the PNPLA2 mutation were summarized. This study suggests that NLSDM should be considered a cause of cardiomyopathy, especially in those with elevated creatine kinase (CK) levels, regardless of whether symptoms such as muscle weakness or atrophy are present.

An important role for triglyceride in regulating spermatogenesis.

Drosophila is a powerful model to study how lipids affect spermatogenesis. Yet, the contribution of neutral lipids, a major lipid group which resides in organelles called lipid droplets (LD), to sperm development is largely unknown. Emerging evidence suggests LD are present in the testis and that loss of neutral lipid- and LD-associated genes causes subfertility; however, key regulators of testis neutral lipids and LD remain unclear. Here, we show LD are present in early-stage somatic and germline cells within the Drosophila testis. We identified a role for triglyceride lipase brummer (bmm) in regulating testis LD, and found that whole-body loss of bmm leads to defects in sperm development. Importantly, these represent cell-autonomous roles for bmm in regulating testis LD and spermatogenesis. Because lipidomic analysis of bmm mutants revealed excess triglyceride accumulation, and spermatogenic defects in bmm mutants were rescued by genetically blocking triglyceride synthesis, our data suggest that bmm-mediated regulation of triglyceride influences sperm development. This identifies triglyceride as an important neutral lipid that contributes to Drosophila sperm development, and reveals a key role for bmm in regulating testis triglyceride levels during spermatogenesis.

Exploring the enigmatic association between PNLIP variants and risk of chronic pancreatitis in a large Chinese cohort.

BACKGROUND & AIMS: Protease-sensitive PNLIP variants were recently associated with chronic pancreatitis (CP) in European populations. The pathological mechanism yet remains elusive. Herein, we performed a comprehensive genetic and functional analysis of PNLIP variants found in a large Chinese cohort, aiming to further unravel the enigmatic association of PNLIP variants with CP. METHODS: All coding and flanking intronic regions of the PNLIP gene were analyzed for rare variants by targeted next-generation sequencing in 1082 Chinese CP patients and 1196 controls. All novel missense variants were subject to analysis of secretion, lipase activity, and proteolytic degradation. One variant was further analyzed for its potential to misfold and induce endoplasmic reticulum (ER) stress. p.F300L, the most common PNLIP variant associated with CP, was used as a control. RESULTS: We identified 12 rare heterozygous PNLIP variants, with 10 being novel. The variant carrier frequency did not differ between the groups. Of them, only the variant p.A433T found in a single patient was considered pathologically relevant. p.A433T exhibited increased susceptibility to proteolytic degradation, which was much milder than p.F300L. Interestingly, both variants exhibited an increased tendency to misfold, leading to intracellular retention as insoluble aggregates, reduced secretion, and elevated ER stress. CONCLUSIONS: Our genetic and functional analysis of PNLIP variants identified in a Chinese CP cohort suggests that the p.A433T variant and the previously identified p.F300L variant are not only protease-sensitive but also may be potentially proteotoxic. Mouse studies of the PNLIP p.F300L and p.A433T variants are needed to clarify their role in CP.

Adipose triglyceride lipase gene expression in peripheral blood mononuclear cells of subjects with obesity and its association with insulin resistance, inflammation and lipid accumulation in liver.

Introduction: Adipose triglyceride lipase (ATGL) is a crucial enzyme responsible for the release of fatty acids from various tissues. The expression of ATGL is regulated by insulin and this enzyme is linked to Insulin resistance (IR). On the other hand, ATGL-mediated lipolysis is connected to macrophage function and thus, ATGL is involved in inflammation and the pathogenesis of lipid-related disorders. This study aimed to investigate the correlation between ATGL, obesity, Metabolic Syndrome (MetS), and inflammation. Methods: A total of 100 participants, including 50 individuals with obesity and 50 healthy participants, were recruited for this study and underwent comprehensive clinical evaluations. Blood samples were collected to measure plasma lipid profiles, glycemic indices, and liver function tests. Additionally, peripheral blood mononuclear cells (PBMCs) were isolated and used for the assessment of the gene expression of ATGL, using real-time PCR. Furthermore, PBMCs were cultured and exposed to lipopolysaccharides (LPS) with simultaneous ATGL inhibition, and the gene expression of inflammatory cytokines, along with the secretion of prostaglandin E2 (PGE2), were measured. Results: The gene expression of ATGL was significantly elevated in PBMCs obtained from participants with obesity and was particularly higher in those diagnosed with MetS. It exhibited a correlation with insulin levels and Homeostatic Model Assessment for IR (HOMA-IR), and it was associated with lipid accumulation in the liver. Stimulation with LPS increased ATGL expression in PBMCs, while inhibition of ATGL attenuated the inflammatory responses induced by LPS. Conclusions: Obesity and MetS were associated with dysregulation of ATGL. ATGL might play a role in the upregulation of inflammatory cytokines and act as a significant contributor to the development of metabolic abnormalities related to obesity.

Renal tubule-specific Atgl deletion links kidney lipid metabolism to glucagon-like peptide 1 and insulin secretion independent of renal inflammation or lipotoxicity.

OBJECTIVE: Lipotoxic injury from renal lipid accumulation in obesity and type 2 diabetes (T2D) is implicated in associated kidney damage. However, models examining effects of renal ectopic lipid accumulation independent of obesity or T2D are lacking. We generated renal tubule-specific adipose triglyceride lipase knockout (RT-SAKO) mice to determine if this targeted triacylglycerol (TAG) over-storage affects glycemic control and kidney health. METHODS: Male and female RT-SAKO mice and their control littermates were tested for changes in glycemic control at 10-12 and 16-18 weeks of age. Markers of kidney health and blood lipid and hormone concentrations were analyzed. Kidney and blood lysophosphatidic acid (LPA) levels were measured, and a role for LPA in mediating impaired glycemic control was evaluated using the LPA receptor 1/3 inhibitor Ki-16425. RESULTS: All groups remained insulin sensitive, but 16- to 18-week-old male RT-SAKO mice became glucose intolerant, without developing kidney inflammation or fibrosis. Rather, these mice displayed lower circulating insulin and glucagon-like peptide 1 (GLP-1) levels. Impaired first-phase glucose-stimulated insulin secretion was detected and restored by Exendin-4. Kidney and blood LPA levels were elevated in older male but not female RT-SAKO mice, associated with increased kidney diacylglycerol kinase epsilon. Inhibition of LPA-mediated signaling restored serum GLP-1 levels, first-phase insulin secretion, and glucose tolerance. CONCLUSIONS: TAG over-storage alone is insufficient to cause renal tubule lipotoxicity. This work is the first to show that endogenously derived LPA modulates GLP-1 levels in vivo, demonstrating a new mechanism of kidney-gut-pancreas crosstalk to regulate insulin secretion and glucose homeostasis.

The critical role of BTRC in hepatic steatosis as an ATGL E3 ligase.

Non-alcoholic fatty liver disease (NAFLD), characterized by hepatic steatosis, is one of the commonest causes of liver dysfunction. Adipose triglyceride lipase (ATGL) is closely related to lipid turnover and hepatic steatosis as the speed-limited triacylglycerol lipase in liver lipolysis. However, the expression and regulation of ATGL in NAFLD remain unclear. Herein, our results showed that ATGL protein levels were decreased in the liver tissues of high-fat diet (HFD)-fed mice, naturally obese mice, and cholangioma/hepatic carcinoma patients with hepatic steatosis, as well as in the oleic acid-induced hepatic steatosis cell model, while ATGL mRNA levels were not changed. ATGL protein was mainly degraded through the proteasome pathway in hepatocytes. Beta-transducin repeat containing (BTRC) was upregulated and negatively correlated with the decreased ATGL level in these hepatic steatosis models. Consequently, BTRC was identified as the E3 ligase for ATGL through predominant ubiquitination at the lysine 135 residue. Moreover, adenovirus-mediated knockdown of BTRC ameliorated steatosis in HFD-fed mouse livers and oleic acid-treated liver cells via upregulating the ATGL level. Taken together, BTRC plays a crucial role in hepatic steatosis as a new ATGL E3 ligase and may serve as a potential therapeutic target for treating NAFLD.

Acute activation of adipocyte lipolysis reveals dynamic lipid remodeling of the hepatic lipidome.

Adipose tissue is the site of long-term energy storage. During the fasting state, exercise, and cold exposure, the white adipose tissue mobilizes energy for peripheral tissues through lipolysis. The mobilization of lipids from white adipose tissue to the liver can lead to excess triglyceride accumulation and fatty liver disease. Although the white adipose tissue is known to release free fatty acids, a comprehensive analysis of lipids mobilized from white adipocytes in vivo has not been completed. In these studies, we provide a comprehensive quantitative analysis of the adipocyte-secreted lipidome and show that there is interorgan crosstalk with liver. Our analysis identifies multiple lipid classes released by adipocytes in response to activation of lipolysis. Time-dependent analysis of the serum lipidome showed that free fatty acids increase within 30 min of ß3-adrenergic receptor activation and subsequently decrease, followed by a rise in serum triglycerides, liver triglycerides, and several ceramide species. The triglyceride composition of liver is enriched for linoleic acid despite higher concentrations of palmitate in the blood. To further validate that these findings were a specific consequence of lipolysis, we generated mice with conditional deletion of adipose tissue triglyceride lipase exclusively in adipocytes. This loss of in vivo adipocyte lipolysis prevented the rise in serum free fatty acids and hepatic triglycerides. Furthermore, conditioned media from adipocytes promotes lipid remodeling in hepatocytes with concomitant changes in genes/pathways mediating lipid utilization. Together, these data highlight critical role of adipocyte lipolysis in interorgan crosstalk between adipocytes and liver.

Unmasking crucial residues in adipose triglyceride lipase for coactivation with comparative gene identification-58.

Lipolysis is an essential metabolic process that releases unesterified fatty acids from neutral lipid stores to maintain energy homeostasis in living organisms. Adipose triglyceride lipase (ATGL) plays a key role in intracellular lipolysis and can be coactivated upon interaction with the protein comparative gene identification-58 (CGI-58). The underlying molecular mechanism of ATGL stimulation by CGI-58 is incompletely understood. Based on analysis of evolutionary conservation, we used site directed mutagenesis to study a C-terminally truncated variant and full-length mouse ATGL providing insights in the protein coactivation on a per-residue level. We identified the region from residues N209-N215 in ATGL as essential for coactivation by CGI-58. ATGL variants with amino acids exchanges in this region were still able to hydrolyze triacylglycerol at the basal level and to interact with CGI-58, yet could not be activated by CGI-58. Our studies also demonstrate that full-length mouse ATGL showed higher tolerance to specific single amino acid exchanges in the N209-N215 region upon CGI-58 coactivation compared to C-terminally truncated ATGL variants. The region is either directly involved in protein-protein interaction or essential for conformational changes required in the coactivation process. Three-dimensional models of the ATGL/CGI-58 complex with the artificial intelligence software AlphaFold demonstrated that a large surface area is involved in the protein-protein interaction. Mapping important amino acids for coactivation of both proteins, ATGL and CGI-58, onto the 3D model of the complex locates these essential amino acids at the predicted ATGL/CGI-58 interface thus strongly corroborating the significance of these residues in CGI-58-mediated coactivation of ATGL.

Medium-chain triglycerides (8:0 and 10:0) increase muscle mass and function in frail older adults: a combined data analysis of clinical trials.

Background: Three clinical trials have examined the chronic effects of medium-chain triglycerides (MCTs) on muscle mass and function in frail older adults (mean age 85 years old). However, significant increases in muscle mass and some muscle function relative to long-chain triglycerides (LCTs) have yet to be shown, possibly due to the small number of participants in each trial. Objective: We re-analyzed these previous clinical trials to clarify whether MCT supplementation can increase muscle mass and function. Analysis: After adding post hoc tests to the original report, we compared changes in measurement between the MCT and LCT groups in the first 2 trials and conducted a combined data analysis. Methods: In a combined data analysis, changes from baseline in measurements at the 3 months intervention in the MCTs- and LCTs-containing groups were assessed by analysis of covariance adjusted for baseline values of each measurement, age, sex, BMI, allocation to trial, habitual intakes in energy, protein, leucine, octanoic acid, decanoic acid, and vitamin D during the baseline period. The Mann-Whitney U test was used to analyze data on right and left knee extension times. Results: MCT supplementation for 3 months increased muscle function relative to LCT supplementation with and without an L-leucine (1.2 g) and vitamin D (cholecalciferol, 20 µg)-enriched supplement. In a combined data analysis (n = 29 in MCTs, n = 27 in LCTs), relative to supplementation with 6 g LCTs/day, supplementation with 6 g MCTs/day at dinner for 3 months significantly increased body weight (adjusted mean change from baseline: MCTs 1.2 vs. LCTs 0.2 kg, p = 0.023), right arm muscle area (MCTs 1.4 vs. LCTs-0.7 cm2, p = 0.002), left calf circumference (p = 0.015), right-hand grip strength (MCTs 1.6 vs. LCTs 0.3 kg, p = 0.017), right knee extension time (p = 0.021), left knee extension time (p = 0.034), walking speed (p = 0.002), and number of iterations in leg open and close test (p < 0.001) and decreased right triceps skinfold thickness (p = 0.016). Conclusion: In frail older adults, supplementation for 3 months with a low dose (6 g/day) of MCTs (C8:0 and C10:0) increased muscle mass and function. These findings indicate the potential for the practical use of MCTs in daily life in treating sarcopenia.

Cooperation of acylglycerol hydrolases in neuronal lipolysis.

Genetic and biochemical evidence has established DDHD-domain containing 2 (DDHD2) as the principal triacylglycerol (TAG) hydrolase in neuronal lipolysis of cytosolic lipid droplets. In this issue of Journal of Lipid Research, Hofer et al. report that DDHD2 cooperates with adipose triglyceride lipase, the principal TAG hydrolase in adipose lipolysis, contributing to cytosolic hydrolysis of both TAG and diacylglycerols in murine neuroblastoma cells and primary cortical neurons via different configurations of the lipases. This finding highlights the complexity of cytosolic acylglycerol hydrolysis and raises many new questions in the field of lipid metabolism.

Sympathetic overdrive and unrestrained adipose lipolysis drive alcohol-induced hepatic steatosis in rodents.

OBJECTIVE: Hepatic steatosis is a key initiating event in the pathogenesis of alcohol-associated liver disease (ALD), the most detrimental organ damage resulting from alcohol use disorder. However, the mechanisms by which alcohol induces steatosis remain incompletely understood. We have previously found that alcohol binging impairs brain insulin action, resulting in increased adipose tissue lipolysis by unrestraining sympathetic nervous system (SNS) outflow. Here, we examined whether an impaired brain-SNS-adipose tissue axis drives hepatic steatosis through unrestrained adipose tissue lipolysis and increased lipid flux to the liver. METHODS: We examined the role of lipolysis, and the brain-SNS-adipose tissue axis and stress in alcohol induced hepatic triglyceride accumulation in a series of rodent models: pharmacological inhibition of the negative regulator of insulin signaling protein-tyrosine phosphatase 1ß (PTP1b) in the rat brain, tyrosine hydroxylase (TH) knockout mice as a pharmacogenetic model of sympathectomy, adipocyte specific adipose triglyceride lipase (ATGL) knockout mice, wildtype (WT) mice treated with ß3 adrenergic agonist or undergoing restraint stress. RESULTS: Intracerebral administration of a PTP1b inhibitor, inhibition of adipose tissue lipolysis and reduction of sympathetic outflow ameliorated alcohol induced steatosis. Conversely, induction of adipose tissue lipolysis through ß3 adrenergic agonism or by restraint stress worsened alcohol induced steatosis. CONCLUSIONS: Brain insulin resistance through upregulation of PTP1b, increased sympathetic activity, and unrestrained adipose tissue lipolysis are key drivers of alcoholic steatosis. Targeting these drivers of steatosis may provide effective therapeutic strategies to ameliorate ALD.

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.

Forkhead box protein O1(FoxO1) is a key cellular regulatory factor that was involved in lipid metabolism in several cell types. This study was performed to explore the regulatory mechanism of FoxO1 in adipose triglyceride lipase (ATGL) promoter-driven transcription during lactation in dairy goats. Chromatin immunoprecipitation (ChIP)-seq and RNA sequencing (RNA-seq) data revealed that FoxO1 was closely related to lipid metabolism and inflammation during lactation in dairy goats. FoxO1 overexpression significantly decreased cellular triglyceride (TAG) content lipid droplet accumulation in goat mammary epithelial cells (GMECs), while ATGL knockdown attenuated this effect of FoxO1. Furthermore, the relative content of free fatty acid (FFAs) was markedly increased in FoxO1-overexpressed cells. Additionally, site-directed mutation and ChIP assays confirmed that FoxO1 promotes ATGL transcription through FoxO1 binding sites (FKH) located in the ATGL promoter. Moreover, insulin attenuated the FoxO1-induced activation of the ATGL promoter. Our data reveal that FoxO1 regulates the activity of ATGL in GMECs by binding to FKH elements located in the ATGL promoter.

Lipid droplets control mitogenic lipid mediator production in human cancer cells.

OBJECTIVES: Polyunsaturated fatty acids (PUFAs) are structural components of membrane phospholipids and precursors of oxygenated lipid mediators with diverse functions, including the control of cell growth, inflammation and tumourigenesis. However, the molecular pathways that control the availability of PUFAs for lipid mediator production are not well understood. Here, we investigated the crosstalk of three pathways in the provision of PUFAs for lipid mediator production: (i) secreted group X phospholipase A2 (GX sPLA2) and (ii) cytosolic group IVA PLA2 (cPLA2α), both mobilizing PUFAs from membrane phospholipids, and (iii) adipose triglyceride lipase (ATGL), which mediates the degradation of triacylglycerols (TAGs) stored in cytosolic lipid droplets (LDs). METHODS: We combined lipidomic and functional analyses in cancer cell line models to dissect the trafficking of PUFAs between membrane phospholipids and LDs and determine the role of these pathways in lipid mediator production, cancer cell proliferation and tumour growth in vivo. RESULTS: We demonstrate that lipid mediator production strongly depends on TAG turnover. GX sPLA2 directs ω-3 and ω-6 PUFAs from membrane phospholipids into TAG stores, whereas ATGL is required for their entry into lipid mediator biosynthetic pathways. ATGL controls the release of PUFAs from LD stores and their conversion into cyclooxygenase- and lipoxygenase-derived lipid mediators under conditions of nutrient sufficiency and during serum starvation. In starving cells, ATGL also promotes the incorporation of LD-derived PUFAs into phospholipids, representing substrates for cPLA2α. Furthermore, we demonstrate that the built-up of TAG stores by acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1) is required for the production of mitogenic lipid signals that promote cancer cell proliferation and tumour growth. CONCLUSION: This study shifts the paradigm of PLA2-driven lipid mediator signalling and identifies LDs as central lipid mediator production hubs. Targeting DGAT1-mediated LD biogenesis is a promising strategy to restrict lipid mediator production and tumour growth.

Novel application potential of cinaciguat in the treatment of mixed hyperlipidemia through targeting PTL/NPC1L1 and alleviating intestinal microbiota dysbiosis and metabolic disorders.

Mixed hyperlipidemia, characterized by high levels of triglycerides and cholesterol, is a key risk factor leading to atherosclerosis and other cardiovascular diseases. Existing clinical drugs usually only work on a single indicator, decreasing either triglyceride or cholesterol levels. Developing dual-acting agents that reduce both triglycerides and cholesterol remains a great challenge. Pancreatic triglyceride lipase (PTL) and Niemann-Pick C1-like 1 (NPC1L1) have been identified as crucial proteins in the transport of triglycerides and cholesterol. Here, cinaciguat, a known agent used in the treatment of acute decompensated heart failure, was identified as a potent dual inhibitor targeting PTL and NPC1L1. We presented in vitro evidence from surface plasmon resonance analysis that cinaciguat interacted with PTL and NPC1L1. Furthermore, cinaciguat exhibited potent PTL-inhibition activity. Fluorescence-labeled cholesterol uptake analysis and confocal imaging showed that cinaciguat effectively inhibited cholesterol uptake. In vivo evaluation showed that cinaciguat significantly reduced the plasma levels of triglycerides and cholesterol, and effectively alleviated high-fat diet-induced intestinal microbiota dysbiosis and metabolic disorders. These results collectively suggest that cinaciguat has the potential to be further developed for the therapy of mixed hyperlipidemia.

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.

Preferential lipolysis of DGAT1 over DGAT2 generated triacylglycerol in Huh7 hepatocytes.

Two distinct diacylglycerol acyltransferases (DGAT1 and DGAT2) catalyze the final committed step of triacylglycerol (TG) synthesis in hepatocytes. After its synthesis in the endoplasmic reticulum (ER) TG is either stored in cytosolic lipid droplets (LDs) or is assembled into very low-density lipoproteins in the ER lumen. TG stored in cytosolic LDs is hydrolyzed by adipose triglyceride lipase (ATGL) and the released fatty acids are converted to energy by oxidation in mitochondria. We hypothesized that targeting/association of ATGL to LDs would differ depending on whether the TG stores were generated through DGAT1 or DGAT2 activities. Individual inhibition of DGAT1 or DGAT2 in Huh7 hepatocytes incubated with oleic acid did not yield differences in TG accretion while combined inhibition of both DGATs completely prevented TG synthesis suggesting that either DGAT can efficiently esterify exogenously supplied fatty acid. DGAT2-made TG was stored in larger LDs, whereas TG formed by DGAT1 accumulated in smaller LDs. Inactivation of DGAT1 or DGAT2 did not alter expression (mRNA or protein) of ATGL, the ATGL activator ABHD5/CGI-58, or LD coat proteins PLIN2 or PLIN5, but inactivation of both DGATs increased PLIN2 abundance despite a dramatic reduction in the number of LDs. ATGL was found to preferentially target to LDs generated by DGAT1 and fatty acids released from TG in these LDs were also preferentially used for fatty acid oxidation. Combined inhibition of DGAT2 and ATGL resulted in larger LDs, suggesting that the smaller size of DGAT1-generated LDs is the result of increased lipolysis of TG in these LDs.

Pharmacological inhibition of lipolysis prevents adverse metabolic outcomes during glucocorticoid administration.

OBJECTIVE: Glucocorticoids are one of the most commonly prescribed classes of anti-inflammatory drugs; however, chronic treatment promotes iatrogenic (drug-induced) diabetes. As part of their physiological role, glucocorticoids stimulate lipolysis to spare glucose. We hypothesized that persistent stimulation of lipolysis during glucocorticoid therapy plays a causative role in the development of iatrogenic diabetes. METHODS: Male C57BL/6J mice were given 100 µg/mL corticosterone (Cort) in the drinking water for two weeks and were fed either normal chow (TekLad 8640) or the same diet supplemented with an adipose triglyceride lipase inhibitor (Atglistatin - 2  g/kg diet) to inhibit the first step of lipolysis. RESULTS: Herein, we report for the first time that glucocorticoid administration promotes a unique state of substrate excess and energetic overload in skeletal muscle that primarily results from the rampant mobilization of endogenous fuels. Inhibiting lipolysis protected mice from Cort-induced gains in fat mass, excess ectopic lipid accrual, hyperinsulinemia, and hyperglycemia. The role lipolysis plays in Cort-mediated pathology appears to differ between tissues. Within skeletal muscle, Cort-induced lipolysis facilitated diversion of glucose-derived carbons toward the pentose phosphate and hexosamine biosynthesis pathways but contributed to <3% of the Cort-induced genomic adaptations. In contrast, Cort stimulation of lipolysis accounted for ∼35% of the genomic changes in the liver but had minimal impact on hepatic metabolites reported. CONCLUSIONS: These data support the idea that activation of lipolysis plays a causal role in the progression toward iatrogenic diabetes during glucocorticoid therapy with differential impact on skeletal muscle and liver.

Nicotinamide mononucleotide induces lipolysis by regulating ATGL expression via the SIRT1-AMPK axis in adipocytes.

Nicotinamide adenine dinucleotide (NAD+) -dependent protein deacetylase SIRT1 plays an important role in the regulation of metabolism. Although the administration of nicotinamide mononucleotide (NMN), a key NAD+ intermediate, has been shown to ameliorate metabolic disorders, such as insulin resistance and glucose intolerance, the direct effect of NMN on the regulation of lipid metabolism in adipocytes remains unclear. We here investigated the effect of NMN on lipid storage in 3T3-L1 differentiated adipocytes. Oil-red O staining showed that NMN treatment reduced lipid accumulation in these cells. NMN was found to enhance lipolysis in adipocytes since the concentration of glycerol in the media was increased by NMN treatment. Western blotting and real-time RT-PCR analysis revealed that adipose triglyceride lipase (ATGL) expression at both protein and mRNA level was increased with NMN treatment in 3T3-L1 adipocytes. Whereas NMN increased SIRT1 expression and AMPK activation, an AMPK inhibitor compound C restored the NMN-dependent upregulation of ATGL expression in these cells, suggesting that NMN upregulates ATGL expression through the SIRT1-AMPK axis. NMN administration significantly decreased subcutaneous fat mass in mice on a high-fat diet. We also found that adipocyte size in subcutaneous fat was decreased with NMN treatment. Consistent with the alteration of fat mass and adipocyte size, the ATGL expression in subcutaneous fat was slightly, albeit significantly, increased with NMN treatment. These results indicate that NMN suppresses subcutaneous fat mass in diet-induced obese mice, potentially in part via the upregulation of ATGL. Unexpectedly, the reduction in fat mass as well as ATGL upregulation with NMN treatment were not observed in epididymal fat, implying that the effects of NMN are site-specific in adipose tissue. Thus, these findings provide important insights into the mechanism of NMN/NAD+ in the regulation of metabolism.