Perilipin A increases triacylglycerol storage by decreasing the rate of triacylglycerol hydrolysis

Molecular adaptation in adipose tissue in response to overfeeding with a high-fat diet under sedentary conditions in South Asian and Caucasian men

For the same BMI, South Asians have a higher body fat percentage than Caucasians. There might be differences in the fatty acid (FA) handling in adipose tissue when both ethnicities are exposed to high-fat overfeeding. The objective of the present study was to investigate the molecular adaptation in relation to FA metabolism in response to overfeeding with a high-fat diet (OHFD) in South Asian and Caucasian men. Ten South Asian men (BMI 18-29 kg/m2) and ten Caucasian men (BMI 22-33 kg/m2), matched for body fat percentage, aged 20-40 years were included. A weight-maintenance diet (30 % fat, 55 % carbohydrate and 15 % protein) was given for 3 d followed by 3 d of overfeeding (150 % energy requirement) with a high-fat diet (60 % fat, 25 % carbohydrate and 15 % protein) while staying in a respiration chamber. Before and after overfeeding, abdominal subcutaneous fat biopsies were taken. Proteins were isolated, analysed and quantified for short-chain 3-hydroxyacyl-CoA dehydrogenase (HADH), carnitine palmitoyl-transferase 1α (CPT1a), adipose TAG lipase, perilipin A (PLINA), perilipin B, lipoprotein lipase and fatty acid binding protein 4 using Western blotting. OHFD decreased the HADH level (P < 0·05) in Caucasians more than in Asians (P < 0·05), but the baseline and after intervention HADH level was relatively higher in Caucasians. The level of CPT1a decreased in South Asians and increased in Caucasians (P < 0·05). PLINA did not change with diet but the level was higher in South Asians (P < 0·05). The observed differences in HADH and PLINA levels as well as in CPT1a response may be important for differences in the long-term regulation of energy (fat) metabolism in these populations.

Additive manufacturing of photo-crosslinked gelatin scaffolds for adipose tissue engineering

There exists a clear clinical need for adipose tissue reconstruction strategies to repair soft tissue defects which outperform the currently available approaches. In this respect, additive manufacturing has shown to be a promising alternative for the development of larger constructs able to support adipose tissue engineering. In the present work, a thiol-ene photo-click crosslinkable gelatin hydrogel was developed which allowed extrusion-based additive manufacturing into porous scaffolds. To this end, norbornene-functionalized gelatin (Gel-NB) was combined with thiolated gelatin (Gel-SH). The application of a macromolecular gelatin-based thiolated crosslinker holds several advantages over conventional crosslinkers including cell-interactivity, less chance at phase separation between scaffold material and crosslinker and the formation of a more homogeneous network. Throughout the paper, these photo-click scaffolds were benchmarked to the conventional methacrylamide-modified gelatin (Gel-MA). The results indicated that stable scaffolds could be realized which were further characterized physico-chemically by performing swelling, mechanical and in vitro biodegradability assays. Furthermore, the seeded adipose tissue-derived stem cells (ASCs) remained viable (>90%) up to 14 days and were able to proliferate. In addition, the cells could be differentiated into the adipogenic lineage on the photo-click crosslinked scaffolds, thereby performing better than the cells supported by the frequently reported Gel-MA scaffolds. As a result, the developed photo-click crosslinked scaffolds can be considered a promising candidate towards adipose tissue engineering and a valuable alternative for the omnipresent Gel-MA. STATEMENT OF SIGNIFICANCE: The field of adipose tissue engineering has emerged as a promising strategy to repair soft tissue defects. Herein, Gel-NB/Gel-SH gelatin-based hydrogel scaffolds were produced using extrusion-based additive manufacturing. Using a cell-interactive, thiolated gelatin crosslinker, a homogeneous network was formed and the risk of phase separation between norbornene-modified gelatin and macromolecular crosslinkers was reduced. UV-induced crosslinking of these materials is based on step growth polymerization which requires less free radicals to enable polymerization. Our results demonstrated the potential of the developed scaffolds, due to their favourable physico-chemical characteristics as well as their adipogenic differentiation potential when benchmarked to Gel-MA scaffolds. Hence, the hydrogels could be of great interest towards future development of adipose tissue constructs and tissue engineering in general.

Intra-Abdominal Fat Adipocyte Hypertrophy through a Progressive Alteration of Lipolysis and Lipogenesis in Metabolic Syndrome Rats

This study evaluates the progressive participation of enzymes involved in lipolysis and lipogenesis, leading to adipocyte hypertrophy in a metabolic syndrome (MS) rat model caused by chronic consumption of 30% sucrose in drinking water. A total of 70 male Wistar rats were divided into two groups: C and MS. Each of these groups were then subdivided into five groups which were sacrificed as paired groups every month from the beginning of the treatment until 5 months. The intra-abdominal fat was dissected, and the adipocytes were extracted. Lipoprotein lipase (LPL), hormone-sensitive lipase (HSL), protein kinases A (PKA), and perilipin A expressions were determined. The LPL and HSL activities were evaluated by spectrophotometry. Histological staining was performed in adipose tissue. Significant increases were observed in blood pressure, HOMA-IR, leptin, triglycerides, insulin, intra-abdominal fat, and number of fat cells per field (p = 0.001) and in advanced glycosylation products, adipocyte area, LPL, HSL activities and/or expression (p ≤ 0.01) in the MS groups progressively from the third month onward. Lipogenesis and lipolysis were increased by LPL activity and HSL activity and/or expression. This was associated with hyperinsulinemia and release of non-esterified fatty acids causing a positive feedback loop that contributes to the development of adipocyte hypertrophy.

Manduca sexta Perilipin 1B: A new PLIN1 isoform linked to fat storage prior to pupation

Perilipins (PLINs) are proteins that associate with lipid droplets (LDs) and play roles in the control of triglycerides (TG) metabolism. Two types of PLINs - 1 and 2- occur in insects. Following previous work on MsPLIN1A (a 42 kDa protein formerly called MsLsd1), here we report a new PLIN1 isoform, MsPLIN1B. MsPLIN1B cDNA was cloned and the 1835bp cDNA contains an ORF encoding a 47.9 kDa protein whose expression was confirmed by mass spectrometry. Alternative transcripts A and B, which differ in the alternative use of exon 1, were the most abundant PLIN1 transcripts in the fat body. These transcripts encode nearly identical proteins except that the B isoform contains 59 additional residues in its amino terminus. No conserved domain was identified in the extra region of MsPLIN1B. The novel PLIN1 isoform is found in lepidopteran species. In Manduca, PLIN1B was expressed only in the 5th instar larva and its levels correlated with fat storage. Furthermore, PLIN1B levels increased with the fat content of the diet in insects of the same age confirming a direct relationship between PLIN1B and TG storage irrespective of development. The nutritional status impacted PLIN1B levels, which decreased in starvation and increased with subsequent re-feeding. Altogether data support a link between PLIN1B and TG storage in caterpillars prior to pupation. The combined findings suggest distinct roles for PLIN1A, PLIN1B and PLIN2. MsPLIN1A abundance correlates with mobilization of TG stores, MsPLIN2 with the synthesis of new LDs and MsPLIN1B abundance correlates with high levels of TG storage and large LD sizes at the end of the last feeding period.

Effects of hypothyroidism on the mesenteric and omental adipose tissue in rats

To characterize the influence of hypothyroidism on the endocrine activity of mesenteric and omental adipose tissue (MOAT) and the peripheral regulation of energy balance (EB) in rats, we analyzed food intake (FI); basal metabolic rate (BMR); locomotor activity; body weight (BW); serum hormone concentrations and the expression of their receptors in MOAT. We evaluated the morphology and differentiation of adipocytes. Hypothyroidism decreased FI, BMR and BW. The percentage of visceral white adipose tissue (WAT) depots and the morphology of adipocytes were similar to euthyroid rats. Serum leptin and adiponectin expression in MOAT were altered by hypothyroidism. The expression of Perilipin 1, HSL, UCP1 and PRDM16 was significantly lower in MOAT of hypothyroid animals. Hypothyroidism in rats leads to a compensated EB by inducing a white adipocyte dysfunction and a decrease in BW, BMR, FI and adipokine secretions without changing the percentage of WAT depots and the morphology of the MOAT.

Perilipin 5 alleviates HCV NS5A-induced lipotoxic injuries in liver

BACKGROUND

The homeostasis of lipid droplets (LDs) plays a crucial role in maintaining the physical metabolic processes in cells, and is regulated by many LD-associated proteins, including perilipin 5 (Plin5) in liver. As the putative sites of hepatitis C virus (HCV) virion assembly, LDs are vital to viral infection. In addition, the hepatic LD metabolism can be disturbed by non-structural HCV proteins, such as NS5A, but the details are still inexplicit.

METHODS

HCV NS5A was overexpressed in the livers and hepatocytes of wild-type and Plin5-null mice. BODIPY 493/503 and oil red O staining were used to detect the lipid content in mouse livers and hepatocytes. The levels of lipids, lipid peroxidation and inflammation biomarkers were further determined. Immunofluorescence assay and co-immunoprecipitation assay were performed to investigate the relationship of Plin5 and NS5A.

RESULTS

One week after adenovirus injection, livers expressing NS5A showed more inflammatory cell aggregation and more severe hepatic injuries in Plin5-null mice than in control mice, which was consistent with the increased serum levels of IL-2 and TNF-α (P < 0.05) observed in Plin5-null mice. Moreover, Plin5 deficiency in the liver and hepatocytes aggravated the elevation of MDA and 4-HNE levels induced by NS5A expression (P < 0.01). The triglyceride (TG) content was increased approximately 25% by NS5A expression in the wild-type liver and hepatocytes but was unchanged in the Plin5-null liver and hepatocytes. More importantly, Plin5 deficiency in the liver and hepatocytes exacerbated the elevation of non-esterified fatty acids (NEFAs) stimulated by NS5A expression (P < 0.05 and 0.01 respectively). Using triacsin C to block acyl-CoA biosynthesis, we found that Plin5 deficiency aggravated the NS5A-induced lipolysis of TG. In contrast, Plin5 overexpression in HepG2 cells ameliorated the NS5A-induced lipolysis and lipotoxic injuries. Immunofluorescent staining demonstrated that NS5A expression stimulated the targeting of Plin5 to the surface of the LDs in hepatocytes without altering the protein levels of Plin5. By co-IP, we found that the N-terminal domain (aa 32-128) of Plin5 was pivotal for its binding with NS5A.

CONCLUSIONS

Our data highlight a protective role of Plin5 against hepatic lipotoxic injuries induced by HCV NS5A, which is helpful for understanding the steatosis and injuries in liver during HCV infection.

Rosiglitazone remodels the lipid droplet and britens human visceral and subcutaneous adipocytes ex vivo

Treatment with PPARγ agonists in vivo improves human adipocyte metabolism, but the cellular mechanisms and possible depot differences in responsiveness to their effects are poorly understood. To examine the ex vivo metabolic effects of rosiglitazone (Rosi), we cultured explants of human visceral (omental) and abdominal subcutaneous adipose tissues for 7 days. Rosi increased mRNA levels of transcriptional regulators of brite/beige adipocytes (PGC1α, PRDM16), triglyceride synthesis (GPAT3, DGAT1), and lipolysis (ATGL) similarly in adipose tissues from both depots. In parallel, Rosi increased key modulators of FA oxidation (UCP1, FABP3, PLIN5 protein), rates of FA oxidation, and protein levels of electron transport complexes, suggesting an enhanced respiratory capacity as confirmed in newly differentiated adipocytes. Rosi led to the formation of small lipid droplets (SLDs) around the adipocyte central lipid droplet; each SLD was decorated with redistributed mitochondria that colocalized with PLIN5. SLD maintenance required lipolysis and FA reesterification. Rosi thus coordinated a structural and metabolic remodeling in adipocytes from both visceral and subcutaneous depots that enhanced oxidative capacity. Selective targeting of these cellular mechanisms to improve adipocyte FA handling may provide a new approach to treat metabolic complications of obesity and diabetes.

Acute intramyocardial lipid accumulation in rats does not slow cardiac conduction per se

Diabetic patients suffer from both cardiac lipid accumulation and an increased risk of arrhythmias and sudden cardiac death. This correlation suggests a link between diabetes induced cardiac steatosis and electrical abnormalities, however, the underlying mechanism remains unknown. We previously showed that cardiac conduction velocity slows in Zucker diabetic fatty rats and in fructose-fat fed rats, models that both exhibit prominent cardiac steatosis. The aim of this study was to investigate whether acute cardiac lipid accumulation reduces conduction velocity per se. Cardiac lipid accumulation was induced acutely by perfusing isolated rat hearts with palmitate-glucose buffer, or subacutely by fasting rats overnight. Subsequently, longitudinal cardiac conduction velocity was measured in right ventricular tissue strips, and intramyocardial triglyceride and lipid droplet content was determined by thin layer chromatography and BODIPY staining, respectively. Perfusion with palmitate-glucose buffer significantly increased intramyocardial triglyceride levels compared to perfusion with glucose (2.16 ± 0.17 (n = 10) vs. 0.92 ± 0.33 nmol/mg WW (n = 9), P < 0.01), but the number of lipid droplets was very low in both groups. Fasting of rats, however, resulted in both significantly elevated intramyocardial triglyceride levels compared to fed rats (3.27 ± 0.43 (n = 10) vs. 1.45 ± 0.24 nmol/mg WW (n = 10)), as well as a larger volume of lipid droplets (0.60 ± 0.13 (n = 10) vs. 0.21 ± 0.06% (n = 10), P < 0.05). There was no significant difference in longitudinal conduction velocity between palmitate-glucose perfused and control hearts (0.77 ± 0.025 (n = 10) vs. 0.75 m/sec ± 0.029 (n = 9)), or between fed and fasted rats (0.75 ± 0.042 m/sec (n = 10) vs. 0.79 ± 0.047 (n = 10)). In conclusion, intramyocardial lipid accumulation does not slow cardiac longitudinal conduction velocity per se. This is true for both increased intramyocardial triglyceride content, induced by palmitate-glucose perfusion, and increased intramyocardial triglyceride and lipid droplet content, generated by fasting.

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

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

Phospholipid synthesis fueled by lipid droplets drives the structural development of poliovirus replication organelles

Rapid development of complex membranous replication structures is a hallmark of picornavirus infections. However, neither the mechanisms underlying such dramatic reorganization of the cellular membrane architecture, nor the specific role of these membranes in the viral life cycle are sufficiently understood. Here we demonstrate that the cellular enzyme CCTα, responsible for the rate-limiting step in phosphatidylcholine synthesis, translocates from the nuclei to the cytoplasm upon infection and associates with the replication membranes, resulting in the rerouting of lipid synthesis from predominantly neutral lipids to phospholipids. The bulk supply of long chain fatty acids necessary to support the activated phospholipid synthesis in infected cells is provided by the hydrolysis of neutral lipids stored in lipid droplets. Such activation of phospholipid synthesis drives the massive membrane remodeling in infected cells. We also show that complex membranous scaffold of replication organelles is not essential for viral RNA replication but is required for protection of virus propagation from the cellular anti-viral response, especially during multi-cycle replication conditions. Inhibition of infection-specific phospholipid synthesis provides a new paradigm for controlling infection not by suppressing viral replication but by making it more visible to the immune system.

Necrosis Driven Triglyceride Synthesis Primes Macrophages for Inflammation During Mycobacterium tuberculosis Infection

Pulmonary tuberculosis (TB) exhibits granulomatous inflammation, a site of controlling bacterial dissemination at the cost of host tissue damage. Intrigued by the granuloma type-dependent expression of inflammatory markers in TB, we sought to investigate underlying metabolic changes that drive amplification of inflammation in TB. Here, we show an association of higher inflammation in necrotic granulomas with the presence of triglyceride (TG)-rich foamy macrophages. The conspicuous absence of these macrophages in solid granulomas identified a link between the ensuing pathology and the metabolic programming of foamy macrophages. Consistent with in vivo findings, in vitro infection of macrophages with Mycobacterium tuberculosis (Mtb) led to increase in TG synthesis only under conditions of ~60% necrosis. Genetic and pharmacologic intervention that reduced necrosis prevented this bystander response. We further demonstrate that necrosis independent of Mtb also elicits the same bystander response in human macrophages. We identified a role for the human enzyme involved in TG synthesis, diacylglycerol O-acyltransferase (DGAT1), in this phenomenon. The increased TG levels in necrosis-associated foamy macrophages promoted the pro-inflammatory state of macrophages to infection while silencing expression of diacylglycerol O-acyltransferase (DGAT1) suppressed expression of pro-inflammatory genes. Our data thus invoke a role for storage lipids in the heightened host inflammatory response during infection-associated necrosis. Our data provide a functional role to macrophage lipid droplets in host defense and open new avenues for developing host-directed therapies against TB.

Normalized neutral lipid quantitation by flow cytometry

Interest in measuring tissue lipids has increased as the link between fat-laden tissues and metabolic disease has become obvious; however, linking disease to a specific cell type within a tissue has been hampered by methodological limitations. Flow cytometry (FC) has been used to assess relative lipid levels in cells. Unfortunately, its usefulness is limited because comparisons between samples generated over several hours is problematic. We show that: 1) in lipophilic fluorophore stained cells, fluorescence intensity measured by FC reflects lipid levels; 2) this technique can be used to assess lipid levels in a mixed cell population; 3) normalizing to a control condition can decrease experiment-to-experiment variation; and 4) fluorescence intensity increases linearly with lipid levels. This allows triacylglycerol (TG) mass to be estimated in mixed cell populations comparing cells with known fluorescence and TG levels. We exploited this strategy to estimate lipid levels in monocytes within a mixed population of cells isolated from human blood. Using this strategy, we also confirmed that perilipin (PLIN)1 increases TG accumulation by ectopically expressing fluorescently tagged PLIN1 in Huh7 cells. In both examples, biochemically assaying for TG in specific cell populations is problematic due to limited cell numbers and isolation challenges. Other advantages are discussed.

Long-term effects of Garcinia cambogia/Glucomannan on weight loss in people with obesity, PLIN4, FTO and Trp64Arg polymorphisms

BACKGROUND

Overweight and obesity are considered major health problems that contribute to increase mortality and quality of life. Both conditions have a high prevalence across the world reaching epidemic numbers. Our aim was to evaluate the effects of the administration of Garcinia cambogia (GC) and Glucomannan (GNN) on long-term weight loss in people with overweight or obesity.

METHODS

Prospective, not-randomized controlled intervention trial was conducted. We treated 214 subjects with overweight or obesity with GC and GNN (500 mg twice a day, each) for 6 months evaluating weight, fat mass, visceral fat, basal metabolic rate, and lipid and glucose blood profiles comparing them with basal values. Some patients were carriers of polymorphisms PLIN4 -11482G > A-, fat mass and obesity-associated (FTO) -rs9939609 A/T- and β-adrenergic receptor 3 (ADRB3) -Trp64Arg.

RESULTS

Treatment produced weight loss, reducing fat mass, visceral fat, lipid and blood glucose profiles while increasing basal metabolic rate. Results were independent of sex, age or suffering from hypertension, diabetes mellitus type 2 or dyslipidemia and were attenuated in carriers of PLIN4, FTO, Trp64Arg polymorphisms.

CONCLUSIONS

Administration of GC and GNN reduce weight and improve lipid and glucose blood profiles in people with overweight or obesity, although the presence of polymorphisms PLIN4, FTO and ADRB3 might hinder in some degree these effects. ISRCTN78807585, 19 September 2017, retrospective study.

Spontaneous development of hepatosteatosis in perilipin-1 null mice with adipose tissue dysfunction

Fatty liver features triglyceride accumulation in hepatocytes and often occurs with obesity and lipodystrophy in humans. Here, we investigated the mechanism of maladaptive hepatosteatosis with adipose-tissue dysfunction. Perilipin 1 (Plin1) did not exist in hepatocytes but was expressed exclusively in adipocytes as a dual modulator for regulating two principal adipose-tissue functions, triglyceride storage and breakdown. Plin1-/- mice showed decreased fat storage but increased lipolysis and efflux of fatty acids from adipose tissue, and hepatosteatosis spontaneously developed without altered circulating inflammatory adipocytokine levels. Plin1-/- adipose dysfunction impaired insulin sensitivity and hepatic glucose metabolism, which might inhibit gluconeogenesis to produce more intermediates for hepatic lipid synthesis. Indeed, the livers of Plin1-/- mice exhibited upregulated mRNA and protein expression of key enzymes and transcriptional factors for the uptake and transport of fatty acids and for de novo synthesis of triglycerides, but the expression of key enzymes and transcriptional factors for fatty-acid oxidation was downregulated. Biochemical assays in Plin1-/- mice confirmed increased fatty acid synthase activity but decreased activity of mitochondrial carnitine palmitoyltransferase 1 and [³H]-palmitate oxidation in the liver. We concluded that dysregulation of two principal functions, adipose storage and hydrolysis, had deleterious consequences on the hepatic lipid metabolism and thereby caused maladaptive hepatosteatosis. This mouse model might mimic and explain the pathogenesis of hepatosteatosis occurring in two typical disorders of adipose tissue dysfunction, obesity and lipodystrophy, particularly in lipodystrophic patients with Plin1 mutation.

Visualization of lipid directed dynamics of perilipin 1 in human primary adipocytes

Perilipin 1 is a lipid droplet coating protein known to regulate lipid metabolism in adipocytes by serving as a physical barrier as well as a recruitment site for lipases to the lipid droplet. Phosphorylation of perilipin 1 by protein kinase A rapidly initiates lipolysis, but the detailed mechanism on how perilipin 1 controls lipolysis is unknown. Here, we identify specific lipid binding properties of perilipin 1 that regulate the dynamics of lipolysis in human primary adipocytes. Cellular imaging combined with biochemical and biophysical analyses demonstrate that perilipin 1 specifically binds to cholesteryl esters, and that their dynamic properties direct segregation of perilipin 1 into topologically distinct micro domains on the lipid droplet. Together, our data points to a simple unifying mechanism that lipid assembly and segregation control lipolysis in human primary adipocytes.

Regulation of TG accumulation and lipid droplet morphology by the novel TLDP1 in Aurantiochytrium limacinum F26-b

Thraustochytrids are marine single-cell protists that produce large amounts of PUFAs, such as DHA. They accumulate PUFAs in lipid droplets (LDs), mainly as constituent(s) of triacylglycerol (TG). We identified a novel protein in the LD fraction of Aurantiochytrium limacinum F26-b using 2D-difference gel electrophoresis. The protein clustered with orthologs of thraustochytrids; however, the cluster was evolutionally different from known PAT family proteins or plant LD protein; thus, we named it thraustochytrid-specific LD protein 1 (TLDP1). TLDP1 surrounded LDs when expressed as a GFP-tagged form. Disruption of the tldp1 gene decreased the content of TG and number of LDs per cell; however, irregular and unusually large LDs were generated in tldp1-deficient mutants. Although the level of TG synthesis was unchanged by the disruption of tldp1, the level of TG degradation was higher in tldp1-deficient mutants than in the WT. These phenotypic abnormalities in tldp1-deficient mutants were restored by the expression of tldp1 These results indicate that TLDP1 is a thraustochytrid-specific LD protein and regulates the TG accumulation and LD morphology in A. limacinum F26-b.

Prior Endurance Training Enhances Beta-Adrenergic Signaling in Epidydimal Adipose from Mice Fed a High-Fat Diet

OBJECTIVE

Adipose tissue beta-adrenergic signaling is attenuated in obesity and insulin resistance. It has been previously demonstrated that prior exercise training protects against short-term, high-fat diet (HFD)-induced weight gain and glucose intolerance. This study aimed to determine whether prior exercise training results in altered beta-adrenergic and lipolytic signaling in adipose tissue when challenged with a HFD.

METHODS

Male C57BL/6J mice underwent 4 weeks of treadmill training (1 h/d, 5 d/wk). Twenty-four hours after the final bout of exercise, mice were fed a HFD (60% kcal lard) for 4 days.

RESULTS

Serum fatty acids, beta-adrenergic signaling (phosphorylated ERK, hormone-sensitive lipase, and p38), and perilipin 1 content were greater in epididymal white adipose tissue (eWAT) from previously trained mice. These changes were not evident in eWAT from trained mice prior to the HFD and were not secondary to alterations in insulin responsiveness or catecholamine concentrations. CL 316,243-mediated increases in hormone-sensitive lipase phosphorylation and fatty acid accumulation in the media were greater in adipose tissue explants from previously trained mice fed a HFD.

CONCLUSIONS

These findings suggest that previous training increases adipose tissue beta-adrenergic responsiveness to a short-term HFD. This may help to explain the protective effect of prior exercise training against the deleterious effects of a HFD.

Lipid Droplet Biogenesis

Lipid droplets (LDs) are ubiquitous organelles that store neutral lipids for energy or membrane synthesis and act as hubs for metabolic processes. Cells generate LDs de novo, converting cells to emulsions with LDs constituting the dispersed oil phase in the aqueous cytoplasm. Here we review our current view of LD biogenesis. We present a model of LD formation from the ER in distinct steps and highlight the biology of proteins that govern this biophysical process. Areas of incomplete knowledge are identified, as are connections with physiology and diseases linked to alterations in LD biology.

The perilipin family of lipid droplet proteins: Gatekeepers of intracellular lipolysis

Lipid droplets in chordates are decorated by two or more members of the perilipin family of lipid droplet surface proteins. The perilipins sequester lipids by protecting lipid droplets from lipase action. Their relative expression and protective nature is adapted to the balance of lipid storage and utilization in specific cells. Most cells of the body have tiny lipid droplets with perilipins 2 and 3 at the surfaces, whereas specialized fat-storing cells with larger lipid droplets also express perilipins 1, 4, and/or 5. Perilipins 1, 2, and 5 modulate lipolysis by controlling the access of lipases and co-factors of lipases to substrate lipids stored within lipid droplets. Although perilipin 2 is relatively permissive to lipolysis, perilipins 1 and 5 have distinct control mechanisms that are altered by phosphorylation. Here we evaluate recent progress toward understanding functions of the perilipins with a focus on their role in regulating lipolysis and autophagy. This article is part of a Special Issue entitled: Recent Advances in Lipid Droplet Biology edited by Rosalind Coleman and Matthijs Hesselink.

Extensive lymph node dissection during pancreaticoduodenectomy: a risk factor for hepatic steatosis?

PURPOSE

The first reports of hepatic steatosis following pancreaticoduodenectomy (PD) were published several years ago; however, clear risk factors remain to be identified. Therefore, the aim of this study was to identify the risk factors for hepatic steatosis post-PD.

METHODS

We studied 90 patients who had undergone PD between September 2005 and January 2015. The inclusion criteria were as follows: available unenhanced CT within one month before PD and at least one unenhanced CT acquisition between PD and chemotherapy initiation. Using scanners, we studied the liver and spleen density as well as the surface areas of visceral (VF) and subcutaneous fat (SCF). These variables were previously identified by univariate and multivariate analyses.

RESULTS

Hepatic steatosis occurred in 25.6% of patients at 45.2 days, on average, post-PD. Among the patients with hepatic steatosis, the average liver density was 52 HU before PD and 15.1 HU post-PD (p < 0.001). The Patients with hepatic steatosis lost more VF (mean, 28 vs. 11 cm²) and SCF (28.8 vs. 13.7 cm²) (p < 0.01 and p = 0.01, respectively). Portal vein resection and extensive lymph node dissection were independent risk factors in the multivariate analysis (odds ratio [OR] 5.29, p = 0.009; OR 3.38, p = 0.04, respectively).

CONCLUSION

Portal vein resection and extensive lymph node dissection are independent risk factors for post-PD hepatic steatosis.

Protein Kinase C β: a New Target Therapy to Prevent the Long-Term Atypical Antipsychotic-Induced Weight Gain

Antipsychotic drugs are currently used in clinical practice for a variety of mental disorders. Among them, clozapine is the most effective medication for treatment-resistant schizophrenia and is most helpful in controlling aggression and the suicidal behavior in schizophrenia and schizoaffective disorder. Although clozapine is associated with a low likelihood of extrapyramidal symptoms and other neurological side effects, it is well known for the weight gain and metabolic side effects, which expose the patient to a greater risk of cardiovascular disorders and premature death, as well as psychosocial issues, leading to non-adherence to therapy. The mechanisms underlying these iatrogenic metabolic disorders are still controversial. We have therefore investigated the in vivo effects of the selective PKCβ inhibitor, ruboxistaurin (LY-333531), in a preclinical model of long-term clozapine-induced weight gain. Cell biology, biochemistry, and behavioral tests have been performed in wild-type and PKCβ knockout mice to investigate the contribution of endogenous PKCβ and its pharmacological inhibition to the psychomotor effects of clozapine. Finally, we also shed light on a novel aspect of the mechanism underlying the clozapine-induced weight gain, demonstrating that the clozapine-dependent PKCβ activation promotes the inhibition of the lipid droplet-selective autophagy process. This paves the way to new therapeutic approaches to this serious complication of clozapine therapy.

Perilipins: a diversity of intracellular lipid droplet proteins

Intracellular lipid droplets (LDs) are found in a wide variety of cell types and have been recognized as organelles with unique spherical structures. Although LDs are not stable lipid-depots, they are active sites of neutral lipid metabolism, and comprise neutral lipid or cholesterol cores surrounded by phospholipid monolayers containing specialized proteins. However, sizes and protein compositions vary between cell and tissue types. Proteins of the perilipin family have been associated with surfaces of LDs and all carry a conserved 11-mer repeat motif. Accumulating evidence indicates that all perilipins are involved in LD formation and that all play roles in LD function under differing conditions. In this brief review, we summarize current knowledge of the roles of perilipins and lipid metabolizing enzymes in a variety of mammalian cell types.

Docosahexaenoic acid increases accumulation of adipocyte triacylglycerol through up-regulation of lipogenic gene expression in pigs

Background

Changing dietary fatty acid composition in modern diet influences the prevalence of obesity. Increasing evidences suggest favorable effects of n-3 PUFA for protecting against obesity and the metabolic syndrome. However, the regulation of n-3 PUFA in adipose is still unclear. Thus, this study addressed metabolism of different dietary fats in the adipose tissue of porcine model.

Methods

Eight-week-old cross-bred pigs were randomly assigned to three groups and fed a 2% fat diet for 30 days from either soybean oil (SBO), docosahexaenoic acid (DHA) or beef tallow. An in vitro experiment was conducted in which linoleic acid (LA), DHA or oleic acid (OA) were added to represent the major fatty acid in the SBO-, DHA- or BT- diets, respectively. Adipocytes size and lipid metabolism related genes were analyzed.

Results

Plasma triacylglycerol (TAG) was lower in DHA- than in BT-fed pigs, and the product of lipolysis, glycerol was highest in BT-fed pigs. In addition, expression of the lipolytic genes, adipose triglyceride lipase and hormone sensitive lipase was higher in BT-fed pigs and with OA treatment in vitro. DHA promoted protein kinase A activity in pigs without affecting lipolytic genes. Adipocyte cell sizes, TAG content and expression of lipogenic-related genes including, adipose differentiated related protein (ADRP) and diacylglycerol acyltransferase 1 (DGAT1) were elevated by DHA in vivo and in vitro, indicating DHA promoted adipogenesis to trap TAG in adipose tissue. Fatty acid β-oxidation genes were increased in the DHA-fed pigs.

Conclusion

This effect was partly explained by the effect of DHA to promote adipogenesis to trap TAG in adipocytes and also increase expression of genes involved in adipocyte fatty acid oxidation. Therefore, our results suggest a direct effect of DHA on adipocyte metabolism, resulting in TAG turnover and fatty acid dissipation to facilitate plasma lipid uptake from the circulation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12944-017-0428-3) contains supplementary material, which is available to authorized users.

Clues on the function of Manduca sexta perilipin 2 inferred from developmental and nutrition-dependent changes in its expression

Cellular triglycerides (TG) are stored in cytosolic lipid droplets (LDs). Perilipins (PLIN) are a group of LD-proteins that play important roles in the assembly and transport of LDs and in TG metabolism. Two members of the PLIN family are found in insects (PLIN1 & 2 or Lsd1 & 2). We have cloned and expressed Manduca sexta PLIN2 (MsPLIN2), and studied developmental and nutritional changes in the expression of PLIN2. Nutritional changes induced fast alterations in PLIN2 mRNA and protein levels in fat body and midgut of the feeding larvae. The relationship observed between PLIN2 expression and TG synthesis in both larval fat body and midgut suggests that PLIN2 is needed when tissues are accumulating TG. However, when the fat body was storing TG at maximal capacity, MsPLIN2 levels declined. This unexpected finding suggests the occurrence of alternative mechanism/s to shield TG from the action of lipases in M. sexta LDs. In addition, it implies that the cellular level of lipid storage could be modulating MsPLIN2 expression and/or degradation. The study also confirmed that MsPLIN2 was most abundant in the adult fat body, which is characterized by a high rate of TG hydrolysis and lipid mobilization. Whether MsPLIN2 is directly involved in lipolysis and/or the secretion of lipids in the fat body of adult of M. sexta is unknown at this time. Nonetheless, the coexistence of high PLIN2 and lipolysis levels suggests a complex role for MsPLIN2. Altogether, we found that MsPLIN2 is needed when the synthesis of glycerides, DG and TG, is active even if the insect is accumulating or consuming TG.

The size matters: regulation of lipid storage by lipid droplet dynamics

Adequate energy storage is essential for sustaining healthy life. Lipid droplet (LD) is the subcellular organelle that stores energy in the form of neutral lipids and releases fatty acids under energy deficient conditions. Energy storage capacity of LDs is primarily dependent on the sizes of LDs. Enlargement and growth of LDs is controlled by two molecular pathways: neutral lipid synthesis and atypical LD fusion. Shrinkage of LDs is mediated by the degradation of neutral lipids under energy demanding conditions and is controlled by neutral cytosolic lipases and lysosomal acidic lipases. In this review, we summarize recent progress regarding the regulatory pathways and molecular mechanisms that control the sizes and the energy storage capacity of LDs.

Role of n-3 Polyunsaturated Fatty Acids in Ameliorating the Obesity-Induced Metabolic Syndrome in Animal Models and Humans

The incidence of obesity and its comorbidities, such as insulin resistance and type II diabetes, are increasing dramatically, perhaps caused by the change in the fatty acid composition of common human diets. Adipose tissue plays a role as the major energy reservoir in the body. An excess of adipose mass accumulation caused by chronic positive energy balance results in obesity. The n-3 polyunsaturated fatty acids (n-3 PUFA), DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid) exert numerous beneficial effects to maintain physiological homeostasis. In the current review, the physiology of n-3 PUFA effects in the body is delineated from studies conducted in both human and animal experiments. Although mechanistic studies in human are limited, numerous studies conducted in animals and models in vitro provide potential molecular mechanisms of the effects of these fatty acids. Three aspects of n-3 PUFA in adipocyte regulation are discussed: (1) lipid metabolism, including adipocyte differentiation, lipolysis and lipogenesis; (2) energy expenditure, such as mitochondrial and peroxisomal fatty acid β-oxidation; and (3) inflammation, including adipokines and specialized pro-resolving lipid mediators. Additionally, the mechanisms by which n-3 PUFA regulate gene expression are highlighted. The beneficial effects of n-3 PUFA may help to reduce the incidence of obesity and its comorbidities.

Adipocyte-specific Hypoxia-inducible gene 2 promotes fat deposition and diet-induced insulin resistance

Objective

Adipose tissue relies on lipid droplet (LD) proteins in its role as a lipid-storing endocrine organ that controls whole body metabolism. Hypoxia-inducible Gene 2 (Hig2) is a recently identified LD-associated protein in hepatocytes that promotes hepatic lipid storage, but its role in the adipocyte had not been investigated. Here we tested the hypothesis that Hig2 localization to LDs in adipocytes promotes adipose tissue lipid deposition and systemic glucose homeostasis.

Method

White and brown adipocyte-deficient (Hig2^fl/fl × Adiponection cre+) and selective brown/beige adipocyte-deficient (Hig2^fl/fl × Ucp1 cre+) mice were generated to investigate the role of Hig2 in adipose depots. Additionally, we used multiple housing temperatures to investigate the role of active brown/beige adipocytes in this process.

Results

Hig2 localized to LDs in SGBS cells, a human adipocyte cell strain. Mice with adipocyte-specific Hig2 deficiency in all adipose depots demonstrated reduced visceral adipose tissue weight and increased glucose tolerance. This metabolic effect could be attributed to brown/beige adipocyte-specific Hig2 deficiency since Hig2^fl/fl × Ucp1 cre+ mice displayed the same phenotype. Furthermore, when adipocyte-deficient Hig2 mice were moved to thermoneutral conditions in which non-shivering thermogenesis is deactivated, these improvements were abrogated and glucose intolerance ensued. Adipocyte-specific Hig2 deficient animals displayed no detectable changes in adipocyte lipolysis or energy expenditure, suggesting that Hig2 may not mediate these metabolic effects by restraining lipolysis in adipocytes.

Conclusions

We conclude that Hig2 localizes to LDs in adipocytes, promoting adipose tissue lipid deposition and that its selective deficiency in active brown/beige adipose tissue mediates improved glucose tolerance at 23 °C. Reversal of this phenotype at thermoneutrality in the absence of detectable changes in energy expenditure, adipose mass, or liver triglyceride suggests that Hig2 deficiency triggers a deleterious endocrine or neuroendocrine pathway emanating from brown/beige fat cells.

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Hig2 localizes to lipid droplets in adipocytes and promotes adipose tissue lipid deposition.

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Its selective deficiency in active brown/beige adipose tissue mediates improved glucose tolerance at 23 °C.

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Metabolic improvements are independent of changes in lipolysis.

Prognostic significance of PLIN1 expression in human breast cancer

Breast cancer is a heterogeneous disease associated with diverse clinical, biological and molecular features, presenting huge challenges for prognosis and treatment. Here we found that perilipin-1 (PLIN1) mRNA expression is significantly downregulated in human breast cancer. Kaplan-Meier analysis indicated that patients presenting with reduced PLIN1 expression exhibited poorer overall metastatic relapse-free survival (p = 0.03). Further Cox proportional hazard models analysis revealed that the reduced expression of PLIN1 is an independent predictor of overall survival in estrogen receptor positive (p < 0.0001, HR = 0.87, 95% CI = 0.81-0.92, N = 3,600) and luminal A-subtype (p = 0.02, HR = 0.88, 95% CI = 0.78-0.98, N = 1,469) breast cancer patients. We also demonstrated that the exogenous expression of PLIN1 in human breast cancer MCF-7 and MDA-MB-231 cells significantly inhibits cell proliferation, migration, invasion and in vivo tumorigenesis in mice. Together, these data provide novel insights into a prognostic significance of PLIN1 in human breast cancer and reveal a potentially new gene therapy target for breast cancer.

Amber Light (590 nm) Induces the Breakdown of Lipid Droplets through Autophagy-Related Lysosomal Degradation in Differentiated Adipocytes

Lipolysis in the adipocytes provides free fatty acids for other tissues in response to the energy demand. With the rapid increase in obesity-related diseases, finding novel stimuli or mechanisms that regulate lipid metabolism becomes important. We examined the effects of visible light (410, 457, 505, 530, 590, and 660 nm) irradiation on lipolysis regulation in adipocytes differentiated from human adipose-derived stem cells (ADSCs). Interestingly, 590 nm (amber) light irradiation significantly reduced the concentration of lipid droplets (LDs). We further investigated the lipolytic signaling pathways that are involved in 590 nm light irradiation-induced breakdown of LDs. Immunoblot analysis revealed that 590 nm light irradiation-induced phosphorylation of hormone-sensitive lipase (HSL) was insufficient to promote reduction of LDs. We observed that 590 nm light irradiation decreased the expression of perilipin 1. We found that 590 nm light irradiation, but not 505 nm, induced conversion of LC3 I to LC3 II, a representative autophagic marker. We further demonstrated that the lysosomal inhibitors leupeptin/NH4Cl inhibited 590 nm light irradiation-induced reduction of LDs in differentiated adipocytes. Our data suggest that 590 nm light irradiation-induced LD breakdown is partially mediated by autophagy-related lysosomal degradation, and can be applied in clinical settings to reduce obesity.

Fluorescent Detection of Lipid Droplets and Associated Proteins

Excess lipid is stored in intracellular organelles known as lipid droplets. This unit discusses techniques for the visualization of lipid droplets and associated proteins in cultured mammalian cells. Protocols for the detection of lipid droplets in fixed or live cells with BODIPY 493/503 are included. The best method for combining visualization of intracellular lipid droplets with indirect immunofluorescent detection of lipid droplet-associated proteins is described. Techniques for sample fixation and permeabilization must be chosen carefully to avoid alterations to lipid droplet morphology. Immunofluorescent detection of perilipin 2, a broadly expressed, lipid droplet-associated protein, widely used as a marker for lipid droplet accumulation, is presented as an example. Finally, a simple protocol for enhancing lipid droplet accumulation through supplementation with excess fatty acid is included. © 2016 by John Wiley & Sons, Inc.

Adipogenic potential of stem cells derived from rabbit subcutaneous and visceral adipose tissue in vitro

Rabbits are considered as appropriate animal models to study some obesity-associated abnormalities because of the similarity of their blood lipid profile and metabolism to humans. The current study was focused on comparison of adipose differentiation ability in rabbit adipose-derived stem cells (ADSC) in vitro. Subcutaneous and visceral stromal vascular fractions (SVF) were isolated from three 28-d-old New Zealand rabbits by collagenase digestion. Supernatants from both isolates were collected 24 h after the initial plating. On the fourth passage, all isolated cell types undergo triplicate adipogenic induction. The adipose induction potential was calculated as percentage of increasing optical density (OD) values. The data revealed that with increasing the number of induction cycles, the induction tendency in visceral ADSC decreased in contrast to the subcutaneous ones. Although the supernatants did not reach induction levels of their relevant precursors, they follow the same pattern in both subcutaneous and visceral ADSC. All cell types successfully passed osteogenic and chondrogenic differentiation. In conclusion, the best adipose induction ability was observed in directly plated subcutaneous cell population. The increase of induction numbers depressed adipose induction ability in cell populations derived from visceral fat depots.

Using fluorescent lipids in live zebrafish larvae: From imaging whole animal physiology to subcellular lipid trafficking

Lipids serve essential functions in cells as signaling molecules, membrane components, and sources of energy. Defects in lipid metabolism are implicated in a number of pandemic human diseases, including diabetes, obesity, and hypercholesterolemia. Many aspects of how fatty acids and cholesterol are absorbed and processed by intestinal cells remain unclear and present a hurdle to developing approaches for disease prevention and treatment. Numerous studies have shown that the zebrafish is an excellent model for vertebrate lipid metabolism. In this chapter, we review commercially available fluorescent lipids that can be deployed in live zebrafish to better understand lipid signaling and metabolism. In this chapter, we present criteria one should consider when selecting specific fluorescent lipids for the study of digestive physiology or lipid metabolism in larval zebrafish.

Adipose tissue depot specific differences of PLIN protein content in endurance trained rats

Adipose tissue is classified as either white (WAT) or brown (BAT) and differs not only by anatomical location but also in function. WAT is the main source of stored energy and releases fatty acids in times of energy demand, whereas BAT plays a role in regulating non-shivering thermogenesis and oxidizes fatty acids released from the lipid droplet. The PLIN family of proteins has recently emerged as being integral in the regulation of fatty acid storage and release in adipose tissue. Previous work has demonstrated that PLIN protein content varies among adipose tissue depots, however an examination of endurance training-induced depot specific changes in PLIN protein expression has yet to be done. Male Sprague-dawley rats (n = 10) underwent 8-weeks of progressive treadmill training (18-25 m/min for 30-60 min at 10% incline) or remained sedentary as control. Following training, under isoflurane induced anesthesia epidydmal (eWAT), inguinal subcutaneous (iWAT) and intrascapular brown adipose tissue (BAT) was excised, and plasma was collected. Endurance training resulted in an increase in BAT PLIN5 and iWAT PLIN3 content, while there was no difference in PLIN protein content in endurance trained eWAT. Interestingly, endurance training resulted in a robust increase in ATGL and CGI-58 in eWAT alone. Together these results suggest the potential of a depot specific function of PLIN3 and PLIN5 in adipose tissue in response to endurance training.

The role of lipid droplet formation in the protection of unsaturated fatty acids against palmitic acid induced lipotoxicity to rat insulin-producing cells

Background

Type 2 diabetes is associated with increased plasma concentrations of non-esterified fatty acids (NEFAs), which trigger pancreatic β-cell dysfunction and apoptosis. Only long-chain saturated NEFAs induced lipotoxicity in rat insulin-producing cells in in vitro experiments, whereas unsaturated NEFAs were not toxic. Some unsaturated NEFAs even protected against lipotoxicity. In former studies it was suggested that long-chain unsaturated NEFAs, which induce the formation of lipid droplets, can cause sequestration of palmitic acid into lipid droplets. In the present structure-activity-relationship study the correlation between lipid droplet formation and the protection against palmitic acid induced lipotoxicity by unsaturated NEFAs in rat insulin-producing cells was examined.

Methods

Rat insulin-producing RINm5F and INS-1E tissue culture cells were incubated in the presence of palmitic acid and unsaturated NEFAs with different chain lengths and different numbers of double bonds. The expression of the lipid droplet associated proteins perilipin 1 and 2 was repressed by the shRNA technique and the expression analyzed by qRT-PCR and Western blotting. Viability was measured by MTT assay and the accumulation of lipid droplets was quantified by fluorescence microscopy after Oil Red O staining.

Results

Long-chain unsaturated NEFAs strongly induce the formation of lipid droplets in rat insulin-producing RINm5F and INS-1E cells. In RINm5F cells incubated with 11-eicosenoic acid (C20:1) 27 % of the cell area was covered by lipid droplets corresponding to a 25-fold increase in comparison with control cells. On the other hand the saturated NEFA palmitic acid only induced minor lipid droplet formation. Viability analyses revealed only a minor toxicity of unsaturated NEFAs, whereas the cells were markedly sensitive to palmitic acid. Long-chain unsaturated NEFAs antagonized palmitic acid induced lipotoxicity during co-incubation, whereby no correlation existed between protection and the ability of lipid droplet formation. Perilipin 1 and 2 expression was decreased after incubation with C20:1 to about 80 % by shRNA. For the protective effect of long-chain unsaturated NEFAs against lipotoxicity of saturated NEFAs repression of perilipin was not of crucial importance.

Conclusions

Long-chain unsaturated fatty acids protected rat insulin-producing cells against lipotoxicity of saturated fatty acids. This protective effect was not dependent on lipid droplet formation. Thus lipid droplet formation is apparently not essential for the protective effect of unsaturated NEFAs against palmitic acid toxicity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0076-z) contains supplementary material, which is available to authorized users.

Bif-1 deficiency impairs lipid homeostasis and causes obesity accompanied by insulin resistance

Bif-1 is a membrane-curvature inducing protein that is implicated in the regulation of autophagy and tumorigenesis. Here, we report that Bif-1 plays a critical role in regulating lipid catabolism to control the size of lipid droplets and prevent the development of obesity and insulin resistance upon aging or dietary challenge. Our data show that Bif-1 deficiency promotes the expansion of adipose tissue mass without altering food intake or physical activities. While Bif-1 is dispensable for adipose tissue development, its deficiency reduces the basal rate of adipose tissue lipolysis and results in adipocyte hypertrophy upon aging. The importance of Bif-1 in lipid turnover is not limited to adipose tissue since fasting and refeeding-induced lipid droplet clearance is also attenuated by Bif-1 loss in the liver. Interestingly, obesity induced by a high fat-diet or Bif-1 deficiency downregulates the expression of proteins involved in the autophagy-lysosomal pathway, including Atg9a and Lamp1 in the adipose tissue. These findings thus identify Bif-1 as a novel regulator of lipid homeostasis to prevent the pathogenesis of obesity and its associated metabolic complications.

Novel flow cytometric approach for the detection of adipocyte subpopulations during adipogenesis

The ability of mesenchymal stromal cells (MSCs) to differentiate into adipocytes provides a cellular model of human origin to study adipogenesis in vitro. One of the major challenges in studying adipogenesis is the lack of tools to identify and monitor the differentiation of various subpopulations within the heterogeneous pool of MSCs. Cluster of differentiation (CD)36 plays an important role in the formation of intracellular lipid droplets, a key characteristic of adipocyte differentiation/maturation. The objective of this study was to develop a reproducible quantitative method to study adipocyte differentiation by comparing two lipophilic dyes [Nile Red (NR) and Bodipy 493/503] in combination with CD36 surface marker staining. We identified a subpopulation of adipose-derived stromal cells that express CD36 at intermediate/high levels and show that combining CD36 cell surface staining with neutral lipid-specific staining allows us to monitor differentiation of adipose-derived stromal cells that express CD36^{intermediate/high} during adipocyte differentiation in vitro. The gradual increase of CD36^{intermediate/high/}NR^positive cells during the 21 day adipogenesis induction period correlated with upregulation of adipogenesis-associated gene expression.

Histocytological specificities of adrenal cortex in the New World Monkeys, Aotus lemurinus and Saimiri boliviensis

The New World monkey Aotus spp. (night monkeys) are expected for use of valuable experimental animal with the close species of Saimiri spp. (squirrel monkeys). Saimiri is known to show spontaneous hypercortisolemia, although few reports in Aotus. We compared basic states of blood steroid hormones and histological structure of the adrenal glands in two monkeys. Serum cortisol and ACTH levels were statistically lower in Aotus than Saimiri. Conversely, Aotus adrenocortical area showed significant enlargement, especially at the zona fasciculata. Electron microscopic observation at Aotus fasciculata cells revealed notable accumulation of large lipid droplets and irregular shapes of the mitochondrial cristae. These results suggest potential differences in cellular activities for steroidogenesis between Aotus and Saimiri and experimental usefulness in adrenocortical physiology and pathological models.

Analysis of biogenesis of lipid droplets by examining Rab40c associating with lipid droplets

The biogenesis of lipid droplets (LDs) is regulated by multiple proteins. Rab40c is a recently characterized small GTPase associating with LDs. Here we describe our approaches to analyze the involvement of Rab40c in the biogenesis of LDs. Co-localization of Rab40c and LDs was revealed through fluorescence confocal microscopy by expressing GFP-Rab40c and labeling LDs with dyes Oil Red O, Nile Red, or BODIPY 493/503. Association of Rab40c with LDs was further confirmed by fractionation with sucrose density centrifugation. The relationship of Rab40c with adipocyte differentiation was examined by detecting the protein level of Rab40c during adipocyte differentiation of 3T3-L1 cells. The roles of Rab40c in the biogenesis of LDs were analyzed by inducing LD formation in HepG2 cells.

Interaction between differential gene expression profile and phenotype in bovine blastocysts originating from oocytes exposed to elevated non-esterified fatty acid concentrations

Maternal metabolic disorders linked to lipolysis are major risk factors for reproductive failure. A notable feature of such disorders is increased non-esterified fatty acid (NEFA) concentrations in the blood, which are reflected in the ovarian follicular fluid. Elevated NEFA concentrations impact on the maturing oocyte and even alter subsequent embryo physiology. The aetiological mechanisms have not been fully elucidated. Therefore, in the present study, bovine in vitro maturing cumulus-oocyte complexes were exposed (24 h) to three different maturation treatments containing: (1) physiological (72 µM) NEFA concentrations (=control); (2) elevated (75 µM) stearic acid (SA) concentrations (=HIGH SA); and (3) elevated (425 µM) NEFA concentrations (=HIGH COMBI). Zygotes were fertilised and cultured following standard procedures. Transcriptomic analyses in resulting Day 7.5 blastocysts revealed that the major pathways affected are related to lipid and carbohydrate metabolism in HIGH COMBI embryos and to lipid metabolism and cell death in HIGH SA embryos. Furthermore, lower glutathione content and a reduced number of lipid droplets per cell were observed in HIGH SA-exposed oocytes and resulting morulae, respectively, compared with their HIGH COMBI-exposed counterparts. Vitrified embryos originating from HIGH SA-exposed oocytes tended to exhibit lower survival rates compared with controls. These data suggest possible mechanisms explaining why females across species suffering lipolytic disorders experience difficulties in conceiving.

Effect of six type II diabetes susceptibility loci and an FTO variant on obesity in Pakistani subjects

The aim of the current study was to analyze the effect of six type II diabetes GWAS loci rs3923113 (GRB14), rs16861329 (ST6GAL1), rs1802295 (VPS26A), rs7178572 (HMG20A), rs2028299 (AP3S2) and rs4812829 (HNF4A), and an FTO polymorphism (rs9939609) on obesity. The probable mechanism of action of these SNPs was analyzed by studying their association with various biochemical and anthropometric parameters. A total of 475 subjects (obese=250, controls=225) were genotyped by TaqMan assay and their lipid profile was determined. Allele/genotype frequencies and an unweighted/weighted gene score were calculated. The effect of the gene score on anthropometric and biochemical parameters was analyzed. The minor allele frequencies of all variants were comparable to that reported in the original studies and were associated with obesity in these Pakistani subjects. Subjects with 9 risk alleles differ from those with <3 and overall there is no significant effect (P-value for trend 0.26). None of the SNPs were associated with any of the serum lipid traits. We are the first to report the association of these T2D SNPs with obesity. In the Pakistani population the reported effect of six SNPs for obesity is similar to that reported for T2D and having a combination of risk alleles on obesity can be considerable. The mechanism of this effect is unclear, but appears not to be mediated by changing serum lipid chemistry.

Adipocyte differentiation-related protein promotes lipid accumulation in goat mammary epithelial cells

Milk fat originates from the secretion of cytosolic lipid droplets (CLD) synthesized within mammary epithelial cells. Adipocyte differentiation-related protein (ADRP; gene symbol PLIN2) is a CLD-binding protein that is crucial for synthesis of mature CLD. Our hypothesis was that ADRP regulates CLD production and metabolism in goat mammary epithelial cells (GMEC) and thus plays a role in determining milk fat content. To understand the role of ADRP in ruminant milk fat metabolism, ADRP (PLIN2) was overexpressed or knocked down in GMEC using an adenovirus system. Immunocytochemical staining revealed that ADRP localized to the surface of CLD. Supplementation with oleic acid (OA) enhanced its colocalization with CLD surface and enhanced lipid accumulation. Overexpression of ADRP increased lipid accumulation and the concentration of triacylglycerol in GMEC. In contrast, morphological examination revealed that knockdown of ADRP decreased lipid accumulation even when OA was supplemented. This response was confirmed by the reduction in mass of cellular TG when ADRP was knocked down. The fact that knockdown of ADRP did not completely eliminate lipid accumulation at a morphological level in GMEC without OA suggests that some other compensatory factors may also aid in the process of CLD formation. The ADRP reversed the decrease of CLD accumulation induced by adipose triglyceride lipase. This is highly suggestive of ADRP promoting triacylglycerol stability within CLD by preventing access to adipose triglyceride lipase. Collectively, these data provide direct in vitro evidence that ADRP plays a key role in CLD formation and stability in GMEC.

Lipid droplet mobilization: The different ways to loosen the purse strings

Cytosolic lipid droplets are dynamic lipid-storage organelles that play a crucial role as reservoirs of metabolic energy and membrane precursors. These organelles are present in virtually all cell types, from unicellular to pluricellular organisms. Despite similar structural organization, lipid droplets are heterogeneous in morphology, distribution and composition. The protein repertoire associated to lipid droplet controls the organelle dynamics. Distinct structural lipid droplet proteins are associated to specific lipolytic pathways. The role of these structural lipid droplet-associated proteins in the control of lipid droplet degradation and lipid store mobilization is discussed. The control of the strictly-regulated lipolysis in lipid-storing tissues is compared between mammals and plants. Differences in the cellular regulation of lipolysis between lipid-storing tissues and other cell types are also discussed.

DAG tales: the multiple faces of diacylglycerol--stereochemistry, metabolism, and signaling

The neutral lipids diacylglycerols (DAGs) are involved in a plethora of metabolic pathways. They function as components of cellular membranes, as building blocks for glycero(phospho)lipids, and as lipid second messengers. Considering their central role in multiple metabolic processes and signaling pathways, cellular DAG levels require a tight regulation to ensure a constant and controlled availability. Interestingly, DAG species are versatile in their chemical structure. Besides the different fatty acid species esterified to the glycerol backbone, DAGs can occur in three different stereo/regioisoforms, each with unique biological properties. Recent scientific advances have revealed that DAG metabolizing enzymes generate and distinguish different DAG isoforms, and that only one DAG isoform holds signaling properties. Herein, we review the current knowledge of DAG stereochemistry and their impact on cellular metabolism and signaling. Further, we describe intracellular DAG turnover and its stereochemistry in a 3-pool model to illustrate the spatial and stereochemical separation and hereby the diversity of cellular DAG metabolism.

Angiotensin II directly impairs adipogenic differentiation of human preadipose cells

Angiotensin II reduces adipogenic differentiation of preadipose cells present in the stroma-vascular fraction of human adipose tissue, which also includes several cell types. Because of the ability of non-adipose lineage cells in the stroma-vascular fraction to respond to angiotensin II, it is not possible to unequivocally ascribe the anti-adipogenic response to a direct effect of this hormone on preadipose cells. Therefore, we used the human Simpson-Golabi-Behmel syndrome (SGBS) preadipocyte cell strain to investigate the consequences of angiotensin II treatment on adipogenic differentiation under serum-free conditions, by assessing expression of typical adipocyte markers perilipin and fatty acid-binding protein 4 (FABP4), at the transcript and protein level. Reverse transcription-polymerase chain reaction showed that perilipin and FABP4 transcripts were, respectively, reduced to 0.33 ± 0.07 (P < 0.05) and 0.41 ± 0.19-fold (P < 0.05) in SGBS cells induced to adipogenic differentiation in the presence of angiotensin II. Western Blot analysis corroborated reduction of the corresponding proteins to 0.23 ± 0.21 (P < 0.01) and 0.46 ± 0.30-fold (P < 0.01) the respective controls without angiotensin II. Angiotensin II also impaired morphological changes associated with early adipogenesis. Hence, we demonstrated that angiotensin II is able to directly reduce adipogenic differentiation of SGBS preadipose cells.