Perilipin overexpression in mice protects against diet-induced obesity

Adipose ZFP36 protects against diet-induced obesity and insulin resistance

AIMS

Obesity, as a worldwide healthcare problem, has become more prevalent. ZFP36 is a well-known RNA-binding protein and involved in the posttranscriptional regulation of many physiological processes. Whether the adipose ZFP36 plays a role in obesity and insulin resistance remains unclear.

METHODS

The expression levels of ZFP36 were analyzed in adipose tissues of obese patients, diet-induced obese mice, ob/ob mice and db/db mice. To determine whether adipose ZFP36 protects against the diet-induced obesity, we generated adipose-specific ZFP36 knockout (ZFP36AKO) mice, which were subjected to high-fat-diet (HFD) for 16 weeks. To explore the specific molecular mechanisms of ZFP36 regulating metabolic disorders, we used gene array assay of control and ZFP36-deficient adipose tissue, and assessed the pathways in vitro and vivo.

RESULTS

Western blotting and RT-PCR were performed to determine the downregulating level of ZFP36 in adipose tissues of obese patients, diet-induced obese mice, ob/ob mice and db/db mice. Relative to control mice, ZFP36AKO mice were more susceptible to HFD-induced obesity, along with insulin resistance, glucose tolerance, and increased metabolic disorders. The obesity of ZFP36AKO mice was attributed to hypertrophy of adipocytes in white adipose tissue via decreased expression of Perilipin1 (PLIN1), adipose triglyceride lipase (ATGL), and hormone-sensitive lipase (HSL). We discovered that ZFP36 oppositely regulated RNF128 expression by repressing the mRNA stability and translation of RNF128, a negative regulator of Sirt1 expression.

CONCLUSIONS

This study suggests that ZFP36 in adipose tissue plays an important role in diet-induced obesity, and identifies a novel molecular signaling pathway of ZFP36/RNF128/Sirt1 involved in obesity.

Effects of duration of high-fat diet on adipocyte hyperplasia in rat epididymis

BACKGROUND

High-fat diet (HFD) contributes to obesity and enhances the expression of mature adipocyte markers. However, the effect of HFD on adipocyte hyperplasia remains controversial. This may be due to variations in the duration of HFD. This study aimed to investigate the effects of different durations of HFD on adipocyte hyperplasia and the expression of mature adipocyte-related markers in obese rats.

METHODS

We divided 32 Sprague-Dawley rats into four groups: B (standard diet control), H1 (HFD for four weeks), H2 (HFD for eight weeks), and H3 (HFD for 12 weeks). We evaluated the morphological changes in epididymal fat cells, measured serum inflammatory markers using enzyme-linked immunosorbent assay (ELISA) kits, and quantified adipocyte hyperplasia and maturation markers using western blotting.

RESULTS

We observed progressive increases in body weight, epididymal fat weight, serum leptin, TNF-α, IL-6, irisin, PPARγ, adiponectin, and FNDC5 protein expression over 8 weeks of HFD. 12 weeks of HFD intervention resulted in significant decreases in irisin, PPARγ, adiponectin, and FNDC5. Concurrently, the expression of perilipin A and ATGL declined with prolonged HFD.

CONCLUSIONS

Our results suggest that the duration of HFD significantly affects adipocyte ability to undergo hyperplasia in the epididymis of obese rats. Specifically, 4 weeks of HFD did not change the capacity for adipocyte hyperplasia, while 8 weeks of the diet enhanced this capacity. Interestingly, a longer diet duration (12 weeks) led to a decrease in adipocyte hyperplasia.

Involvement of a battery of investigated genes in lipid droplet pathophysiology and associated comorbidities

Lipid droplets (LDs) are highly specialized energy storage organelles involved in the maintenance of lipid homoeostasis by regulating lipid flux within white adipose tissue (WAT). The physiological function of adipocytes and LDs can be compromised by mutations in several genes, leading to NEFA-induced lipotoxicity, which ultimately manifests as metabolic complications, predominantly in the form of dyslipidemia, ectopic fat accumulation, and insulin resistance. In this review, we delineate the effects of mutations and deficiencies in genes - CIDEC, PPARG, BSCL2, AGPAT2, PLIN1, LIPE, LMNA, CAV1, CEACAM1, and INSR - involved in lipid droplet metabolism and their associated pathophysiological impairments, highlighting their roles in the development of lipodystrophies and metabolic dysfunction.

Preliminary investigation on the establishment of a new meibomian gland obstruction model and gene expression

Meibomian gland dysfunction is a chronic ocular surface disease with a complex pathogenesis, whose main clinical manifestations are meibomian gland obstruction or/and lipid abnormalities. To explore the mechanism of MGD due to meibomian gland obstruction (MGO), we established a rat model of MGO by cauterizing the meibomian gland orifice. The morphology of the lid margins and meibomian gland orifices were visualized by slit lamp. The tear production of rats was measured by phenol red cotton thread, the tear film breakup time and corneal fluorescein staining scores of rats were detected under cobalt blue light of slit lamp. Changes in the histological structure of the meibomian gland (MG) were observed by HE staining, Oil Red O staining and immunofluorescence staining (collagen IV). RNA sequencing was used to detect differentially expressed genes in MGO and normal rats, which were validated by qPCR. In the MGO group after 4, 8, and 16 weeks, the meibomian gland orifices were closed, tear film break-up time decreased and corneal fluorescein staining score increased (p < 0.05). MG acini was smaller at 8-week and 16-week MGO rats in HE staining. Oil Red O staining showed less condensed staining in the 8- and 16-week MGO groups, while more condensed staining in the 4-week MGO group. Additionally, the basement membrane was destroyed in 16-week MGO group by immunofluorescence staining of collagen IV. Meanwhile, RNA sequencing and qPCR showed that lipid peroxidation (LPO), transient receptor potential vanilloid-3 (TRPV3) and genes in PPAR signaling pathway were differentially expressed in 16-week meibomian gland obstructive rats (p < 0.05). Consequently, meibomian gland obstruction model rats were established successfully with corneal damage and lower tear film stability. Meibomian gland obstruction is a causative factor of MGD, which led to abnormal histological structure in MG, differential expression of PPAR signaling pathway and TRPV3.

Perilipins: A family of five fat-droplet storing proteins that play a significant role in fat homeostasis

Lipid droplets are organelles with unique spherical structures. They consist of a hydrophobic neutral lipid core that varies depending on the cell type and tissue. These droplets are surrounded by phospholipid monolayers, along with heterogeneous proteins responsible for neutral lipid synthesis and metabolism. Additionally, there are specialized lipid droplet-associated surface proteins. Recent evidence suggests that proteins from the perilipin family (PLIN) are associated with the surface of lipid droplets and are involved in their formation. These proteins have specific roles in hepatic lipid droplet metabolism, such as protecting the lipid droplets from lipase action and maintaining a balance between lipid storage and utilization in specific cells. Metabolic dysfunction-associated steatotic liver disease (MASLD) is characterized by the accumulation of lipid droplets in more than 5% of the hepatocytes. This accumulation can progress into metabolic dysfunction-associated steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. The accumulation of hepatic lipid droplets in the liver is associated with the progression of MASLD and other diseases such as sarcopenic obesity. Therefore, it is crucial to understand the role of perilipins in this accumulation, as these proteins are key targets for developing novel therapeutic strategies. This comprehensive review aims to summarize the structure and characteristics of PLIN proteins, as well as their pathogenic role in the development of hepatic steatosis and fatty liver diseases.

Improving obesity research: Unveiling metabolic pathways through a 3D In vitro model of adipocytes using 3T3-L1 cells

Obesity, a burgeoning global health crisis, has tripled in prevalence over the past 45 years, necessitating innovative research methodologies. Adipocytes, which are responsible for energy storage, play a central role in obesity. However, most studies in this field rely on animal models or adipocyte monolayer cell cultures, which are limited in their ability to fully mimic the complex physiology of a living organism, or pose challenges in terms of cost, time consumption, and ethical considerations. These limitations prompt a shift towards alternative methodologies. In response, here we show a 3D in vitro model utilizing the 3T3-L1 cell line, aimed at faithfully replicating the metabolic intricacies of adipocytes in vivo. Using a workable cell line (3T3-L1), we produced adipocyte spheroids and differentiated them in presence and absence of TNF-α. Through a meticulous proteomic analysis, we compared the molecular profile of our adipose spheroids with that of adipose tissue from lean and obese C57BL/6J mice. This comparison demonstrated the model's efficacy in studying metabolic conditions, with TNF-α treated spheroids displaying a notable resemblance to obese white adipose tissue. Our findings underscore the model's simplicity, reproducibility, and cost-effectiveness, positioning it as a robust tool for authentically mimicking in vitro metabolic features of real adipose tissue. Notably, our model encapsulates key aspects of obesity, including insulin resistance and an obesity profile. This innovative approach has the potential to significantly impact the discovery of novel therapeutic interventions for metabolic syndrome and obesity. By providing a nuanced understanding of metabolic conditions, our 3D model stands as a transformative contribution to in vitro research, offering a pathway for the development of small molecules and biologics targeting these pervasive health issues in humans.

Molecular mechanisms of perilipin protein function in lipid droplet metabolism

Perilipins are abundant lipid droplet (LD) proteins present in all metazoans and also in Amoebozoa and fungi. Humans express five perilipins, which share a similar domain organization: an amino-terminal PAT domain and an 11-mer repeat region, which can fold into amphipathic helices that interact with LDs, followed by a structured carboxy-terminal domain. Variations of this organization that arose during vertebrate evolution allow for functional specialization between perilipins in relation to the metabolic needs of different tissues. We discuss how different features of perilipins influence their interaction with LDs and their cellular targeting. PLIN1 and PLIN5 play a direct role in lipolysis by regulating the recruitment of lipases to LDs and LD interaction with mitochondria. Other perilipins, particularly PLIN2, appear to protect LDs from lipolysis, but the molecular mechanism is not clear. PLIN4 stands out with its long repetitive region, whereas PLIN3 is most widely expressed and is used as a nascent LD marker. Finally, we discuss the genetic variability in perilipins in connection with metabolic disease, prominent for PLIN1 and PLIN4, underlying the importance of understanding the molecular function of perilipins.

Mutational scanning pinpoints distinct binding sites of key ATGL regulators in lipolysis

ATGL is a key enzyme in intracellular lipolysis and plays an important role in metabolic and cardiovascular diseases. ATGL is tightly regulated by a known set of protein-protein interaction partners with activating or inhibiting functions in the control of lipolysis. Here, we use deep mutational protein interaction perturbation scanning and generate comprehensive profiles of single amino acid variants that affect the interactions of ATGL with its regulatory partners: CGI-58, G0S2, PLIN1, PLIN5 and CIDEC. Twenty-three ATGL amino acid variants yield a specific interaction perturbation pattern when validated in co-immunoprecipitation experiments in mammalian cells. We identify and characterize eleven highly selective ATGL switch mutations which affect the interaction of one of the five partners without affecting the others. Switch mutations thus provide distinct interaction determinants for ATGL's key regulatory proteins at an amino acid resolution. When we test triglyceride hydrolase activity in vitro and lipolysis in cells, the activity patterns of the ATGL switch variants trace to their protein interaction profile. In the context of structural data, the integration of variant binding and activity profiles provides insights into the regulation of lipolysis and the impact of mutations in human disease.

Effects of Ecklonia stolonifera Extract on Metabolic Dysregulation in High-Fat Diet-Induced Obese Mice

This study aimed to test the hypothesis that long-term and low-dose supplementation with an ethanol extract of Ecklonia stolonifera may confer protection against high-fat diet (HFD)-induced obesity in mice. Male C57BL/6J mice were divided into two groups, one of which was fed an HFD (40 kcal% fat) and the other an HFD+E. stolonifera (0.006%, w/w, ∼5 mg/kg body weight/day) for 16 weeks. E. stolonifera supplementation significantly reduced body weight from week 3 and until the end of the experiment. E. stolonifera-supplemented mice also exhibited lower fat mass (epididymal, perirenal, and mesenteric fat) and smaller adipocyte size than HFD control mice. The two groups displayed similar food intakes, but E. stolonifera markedly decreased lipogenesis and increased lipolysis and fatty acid oxidation in adipose tissue. Moreover, E. stolonifera significantly decreased plasma and hepatic lipid levels, hepatic lipid droplet accumulation, plasma aminotransferase levels, and liver weight by decreasing lipogenesis and increasing fatty acid oxidation. As E. stolonifera-supplemented mice showed improvements in hyperglycemia, insulin resistance, and inflammation, compared to control mice, it is possible that the beneficial effects of E. stolonifera on obesity might be associated with decreased inflammation and insulin resistance. Collectively, these results indicate that E. stolonifera could be used as a novel means of preventing and treating obesity and obesity-related metabolic disorders.

ApoL6 associates with lipid droplets and disrupts Perilipin1-HSL interaction to inhibit lipolysis

Adipose tissue stores triacylglycerol (TAG) in lipid droplets (LD) and release fatty acids upon lipolysis during energy shortage. We identify ApoL6 as a LD-associated protein mainly found in adipose tissue, specifically in adipocytes. ApoL6 expression is low during fasting but induced upon feeding. ApoL6 knockdown results in smaller LD with lower TAG content in adipocytes, while ApoL6 overexpression causes larger LD with higher TAG content. We show that the ApoL6 affects adipocytes through inhibition of lipolysis. While ApoL6, Perilipin 1 (Plin1), and HSL can form a complex on LD, C-terminal ApoL6 directly interacts with N-terminal Plin1 to prevent Plin1 binding to HSL, to inhibit lipolysis. Thus, ApoL6 ablation decreases white adipose tissue mass, protecting mice from diet-induced obesity, while ApoL6 overexpression in adipose brings obesity and insulin resistance, making ApoL6 a potential future target against obesity and diabetes.

Comprehensive analysis of transcriptomic and metabolomic profiles uncovered the age-induced dynamic development pattern of subcutaneous fat in Ningxiang pig

Enhancing meat production and quality is the eternal theme for pig breeding industries. Fat deposition has always been the focus of research in practical production because it is closely linked to pig production efficiency and pork quality. In the current study, multi-omics techniques were performed to explore the modulatory mechanisms of backfat (BF) accumulation at three core developmental stages for Ningxiang pigs. Our results identified that 15 differentially expressed genes (DEGs) and 9 significantly changed metabolites (SCMs) contributed to the BF development via the cAMP signaling pathway, regulation of lipolysis in adipocytes, and biosynthesis of unsaturated fatty acids. Herein, we found a series of candidate genes such as adrenoceptor beta 1 (ADRB1), adenylate cyclase 5 (ADCY5), ATPase Na+/K+ transporting subunit beta 1 (ATP1B1), ATPase plasma membrane Ca2+ transporting 3 (ATP2B3), ATPase Na+/K+ transporting subunit alpha 2 (ATP1A2), perilipin 1 (PLIN1), patatin like phospholipase domain containing 3 (PNPLA3), ELOVL fatty acid elongase 5 (ELOVL5) and metabolites like epinephrine, cAMP, arachidonic acid, oleic acid, linoleic acid, and docosahexaenoic acid existed age-specificeffects and played important roles in lipolysis, fat accumulation, and fatty acid composition. Our findings provide a reference for molecular mechanisms in BF tissue development and the optimization of carcass quality.

Challenges in Pharmacological Intervention in Perilipins (PLINs) to Modulate Lipid Droplet Dynamics in Obesity and Cancer

Perilipins (PLINs) are the most abundant proteins in lipid droplets (LD). These LD-associated proteins are responsible for upgrading LD from inert lipid storage structures to fully functional organelles, fundamentally integrated in the lipid metabolism. There are five distinct perilipins (PLIN1-5), each with specific expression patterns and metabolic activation, but all capable of regulating the activity of lipases on LD. This plurality creates a complex orchestrated mechanism that is directly related to the healthy balance between lipogenesis and lipolysis. Given the essential role of PLINs in the modulation of the lipid metabolism, these proteins can become interesting targets for the treatment of lipid-associated diseases. Since reprogrammed lipid metabolism is a recognized cancer hallmark, and obesity is a known risk factor for cancer and other comorbidities, the modulation of PLINs could either improve existing treatments or create new opportunities for the treatment of these diseases. Even though PLINs have not been, so far, directly considered for pharmacological interventions, there are many established drugs that can modulate PLINs activity. Therefore, the aim of this study is to assess the involvement of PLINs in diseases related to lipid metabolism dysregulation and whether PLINs can be viewed as potential therapeutic targets for cancer and obesity.

Effect of Crocetin on Basal Lipolysis in 3T3-L1 Adipocytes

Crocetin (CCT) is a natural saffron-derived apocarotenoid that possesses healthy properties such as anti-adipogenic, anti-inflammatory, and antioxidant activities. Lipolysis is enhanced in obesity and correlates with a pro-inflammatory, pro-oxidant state. In this context, we aimed to investigate whether CCT affects lipolysis. To evaluate CCT's possible lipolytic effect, 3T3-L1 adipocytes were treated with CCT10μM at day 5 post-differentiation. Glycerol content and antioxidant activity were assessed using colorimetric assays. Gene expression was measured using qRT-PCR to evaluate the effect of CCT on key lipolytic enzymes and on nitric oxide synthase (NOS) expression. Total lipid accumulation was assessed using Oil Red O staining. CCT10μM decreased glycerol release from 3T3-L1 adipocytes and downregulated adipose tissue triglyceride lipase (ATGL) and perilipin-1, but not hormone-sensitive lipase (HSL), suggesting an anti-lipolytic effect. CCT increased catalase (CAT) and superoxide dismutase (SOD) activity, thus showing an antioxidant effect. In addition, CCT exhibited an anti-inflammatory profile, i.e., diminished inducible NOS (NOS2) and resistin expression, while enhanced the expression of adiponectin. CCT10μM also decreased intracellular fat and C/EBPα expression (a transcription factor involved in adipogenesis), thus revealing an anti-adipogenic effect. These findings point to CCT as a promising biocompound for improving lipid mobilisation in obesity.

Lipid Droplet Protein PLIN1 Regulates Inflammatory Polarity in Human Macrophages and is Involved in Atherosclerotic Plaque Development by Promoting Stable Lipid Storage

AIM

Perilipins (PLINs), peripheral lipid droplet (LD) proteins, play important roles in lipid accumulation and maturation in adipocytes. The relationship between PLIN family proteins and macrophage polarization in atherosclerosis has not been elucidated.

METHODS

The experiments used tissues from human arteries of 65 patients who had undergone a carotid endarterectomy, and cultured macrophages generated from healthy human peripheral blood mononuclear cells.

RESULTS

Plaque immunohistochemistry demonstrated co-expression of PLIN1 and PLIN2 in both symptomatic (n=31) and asymptomatic patients (n=34). PLIN2 mRNA expression increased 3.38-fold in the symptomatic group compared with those from asymptomatic. PLIN1 was not expressed on small LDs at a shorter incubation but was on large LDs at longer incubation with oxidized LDL and VLDL, while PLIN2 was observed after 24 h and increased with a longer incubation in cultured M1 macrophage. In M2 macrophages, PLIN1 was seen as early as 24 h following incubation with VLDL, and LD size increased with longer incubation. PLIN1 overexpression increased the size of LDs in M1 macrophages, even after a short incubation, and reduced the RNA expression of TNFA, MMP2, ABCA1, and ABCG1 versus the M1 control. Conversely, silencing of PLIN1 in M2 macrophages had the opposite effects on LD size and RNA expression.

CONCLUSION

There was a relationship between macrophage polarity, cytosolic LD size, and PLIN1/PLIN2 expression levels. PLIN2 was mainly expressed in arterial plaques in symptomatic stroke patients, and associated with the inflammatory phenotype of human macrophages, while PLIN1 expression is closely associated with plaque stability and the anti-inflammatory phenotype.

Polymorphism PLIN1 11482 G>A interacts with dietary intake to modulate anthropometric measures and lipid profile in adults with normal-weight obesity syndrome

Evidence shows that genetic polymorphisms in perilipin 1 gene (PLIN1) are associated with excessive accumulation of body fat and disturbances in cardiometabolic markers. Therefore, the aim of this study was to verify whether the SNP PLIN1 11482 G>A (rs894160) interacts with nutrient intake, anthropometric, body composition and cardiometabolic markers in adults with normal-weight obesity (NWO) syndrome. A cross-sectional study was carried out with 116 individuals aged 20-59 years, with normal BMI and high percentage of body fat. Anthropometric and body composition measures, glycaemic control and serum lipid markers, SNP PLIN1 11482 G>A and nutrient intake were evaluated. Interactions between nutrient intake and the SNP were determined by regression models and adjusted for potential confounders. The SNP frequency was 56·0 % GG, 38·8 % GA and 5·2 % AA. Anthropometric measures and biochemical markers were not different according to genotype, except for total cholesterol (TC), LDL-cholesterol and non-HDL-cholesterol concentrations. However, important interactions between the SNP and dietary intake were observed. Carbohydrate intake interacted with the SNP PLIN1 11482 G>A to modulate waist circumference (WC) and the homeostatic model assessment of insulin resistance index. Interaction of lipid intake and the SNP modulated TC and LDL-cholesterol concentrations, and the interaction between protein intake and the SNP tended to modulate weight, WC and BMI. The SNP PLIN1 11482 G>A seems to modulate responses in anthropometric and lipid profile biomarkers of subjects with NWO depending on the dietary macronutrient composition, which may have long-term impact on cardiometabolic markers.

The diabetogenic effects of chronic supplementation of vitamin C or E in rats: Interplay between liver and adipose tissues transcriptional machinery of lipid metabolism

AIM

The chronic administration of vitamin C and E can differentially disrupt hepatic insulin molecular pathway in rats. Hence, this study evaluated their effects on lipogenesis in the liver and adipose tissue and investigated the possible involvement of microRNA (miR)-22/29a/27a in the induced impaired glucose tolerance.

MAIN METHODS

Wistar rats were orally supplemented with vitamin C (100, 200, and 500 mg/kg) or vitamin E (50, 100, and 200 mg/kg) for eight months.

KEY FINDINGS

Vitamin C or E at the highest doses significantly altered liver weight and index, serum and hepatic lipids, adiponectin, and liver enzymes; besides their reported unfavorable effect on glucose homeostasis. Vitamin C and E negatively affected peroxisome proliferator-activated receptor coactivator-1 (PGC-1α), sterol regulatory element-binding protein (SREBP)-1c/-2, miR-22/29a/27a expression, and adipose perilipin 1 to different extents, effects that were supported by the histopathological examination.

SIGNIFICANCE

The current study provides a deeper insight into the findings of our previous study and highlights the detrimental effects of chronic vitamins supplementation on lipid metabolism. Overall, these findings emphasize the damage caused by the mindless use of supplements and reinforce the role of strict medical monitoring, particularly during the new COVID-19 era during which numerous commercial supplements are claiming to improve immunity.

Liver Transcriptome and Gut Microbiome Analysis Reveals the Effects of High Fructose Corn Syrup in Mice

High fructose corn syrup (HFCS) is a viscous mixture of glucose and fructose that is used primarily as a food additive. This article explored the effect of HFCS on lipid metabolism-expressed genes and the mouse gut microbiome. In total, ten 3-week-old male C57BL/6J mice were randomly divided into two groups, including the control group, given purified water (Group C) and 30% HFCS in water (Group H) for 16 weeks. Liver and colonic content were collected for transcriptome sequencing and 16S rRNA gene sequencing, respectively. HFCS significantly increased body weight, epididymal, perirenal fat weight in mice (p < 0.05), and the proportion of lipid droplets in liver tissue. The expression of the ELOVL fatty acid elongase 3 (Elovl3) gene was reduced, while Stearoyl-Coenzyme A desaturase 1 (Scd1), peroxisome proliferator activated receptor gamma (Pparg), fatty acid desaturase 2 (Fads2), acyl-CoA thioesterase 2 (Acot2), acyl-CoA thioesterase 2 (Acot3), acyl-CoA thioesterase 4 (Acot4), and fatty acid binding protein 2 (Fabp2) was increased in Group H. Compared with Group C, the abundance of Firmicutes was decreased in Group H, while the abundance of Bacteroidetes was increased, and the ratio of Firmicutes/Bacteroidetes was obviously decreased. At the genus level, the relative abundance of Bifidobacterium, Lactobacillus, Faecalibaculum, Erysipelatoclostridium, and Parasutterella was increased in Group H, whereas that of Staphylococcus, Peptococcus, Parabacteroides, Donghicola, and Turicibacter was reduced in Group H. Pparg, Acot2, Acot3, and Scd1 were positively correlated with Erysipelatoclostridium and negatively correlated with Parabacteroides, Staphylococcus, and Turicibacter. Bifidobacterium was negatively correlated with Elovl3. Overall, HFCS affects body lipid metabolism by affecting the expression of lipid metabolism genes in the liver through the gut microbiome.

Perilipin Genetic Variation Correlated with Obesity and Lipid Profile in Metabolic Syndrome

BACKGROUND: Perilipin is very important for the regulation of the deposition and mobilization of fats. The human perilipin gene (PLIN) is near the locus for risk of obesity and hypertriglyceridemia. The PLIN gene is thought to be involved in the occurrence of metabolic syndrome. AIM: The aim of this research is to determine the role of variations of the PLIN gene (PLN4 11482 G>A) as a risk factor for component of metabolic syndrome. METHODS: This study involved a total of 160 subjects consisting of 80 with metabolic syndrome and 80 controls. Genotype analysis was done with the polymerase chain reaction-restriction fragment length polymorphism method. The data were analyzed with t-tests to compare the subjects’ characteristics between metabolic syndrome groups and controls. Risk factors of PLIN genotypes were calculated with odds ratio and multivariate regression analysis was used to determine the role of the PLIN gene with each biochemical characteristic. RESULTS: The result was significant differences between the characteristics of the metabolic syndrome subjects with controls (p < 0.05). There was no difference in genotypes between patients with metabolic syndrome and controls. The multivariate analysis of the genetic role with biochemical components showed the PLIN gene in AA carriers as a risk factor for metabolic syndrome compare GA+GG, risk of obesity, and hypercholesterolemia with p < 0.05. CONCLUSION: It can be concluded that PLIN variation has a role in the incidence of metabolic syndrome, especially in relation to obesity and hypercholesterolemia. Further study is needed to determine the role of other gene variations as a risk factor for metabolic syndrome.

Perilipins at a glance

Lipid droplets (LDs) are ubiquitous organelles that store and supply lipids for energy metabolism, membrane synthesis and production of lipid-derived signaling molecules. While compositional differences in the phospholipid monolayer or neutral lipid core of LDs impact their metabolism and function, the proteome of LDs has emerged as a major influencer in all aspects of LD biology. The perilipins (PLINs) are the most studied and abundant proteins residing on the LD surface. This Cell Science at a Glance and the accompanying poster summarize our current knowledge of the common and unique features of the mammalian PLIN family of proteins, the mechanisms through which they affect cell metabolism and signaling, and their links to disease.

Losartan Attenuates Insulin Resistance and Regulates Browning Phenomenon of White Adipose Tissue in ob/ob Mice

Insulin resistance (IR) is a villain role to the pathology of fatty liver diseases implicated in adipose tissue dysfunction, which is characterized by lipid droplets (LDs) accumulation and hypoxia-inducible factor 1α (HIF1α) related macrophage infiltration. HIF1α is required for its lipogenic actions in adipocytes, while and it regulates M1 and M2 polarization features of macrophages. Losartan has been shown to be an insulin sensitizer in obese states, actions involving in HIF1α signaling. However, the exact mechanisms accounting for these effects have not been fully elucidated. Therefore, GTT, ITT, and HOMA-IR were identified losartan alleviated IR signaling in obese mice. This alleviation may through inhibits HIF1α by suppressing STAT3-NF-κB signaling, which, in turn, revealed HIF1α-dependent decreases the angiogenesis pathway in adipose tissue, including regulation of VEGF and TGFβR2 levels. In white adipose tissue, a set of lipogenesis-related genes, Srebp1, Fas, and Scd-1 were markedly downregulated after losartan intervention, as well as reduced LDs size and LD-associated proteins, perilipin family proteins (PLINs) compared with obese mice. Losartan abolished macrophage infiltration with upregulation of M2 and inhibition of M1 macrophage markers in obese mice. Our data suggest that losartan attenuated obese-induced fatty liver, linked to alleviating inflammation in adipose tissues and a shift in M1/M2 macrophage balance. Furthermore, losartan might improve mitochondria biogenesis by upregulating SIRT1, PGC1α, UCP1, and mRNA of Tfam, Cd137, Tmem26, Ucp1 expression in white adipose tissue compared with the obese group. Taken together, losartan may improve IR and adipose dysfunction by inhibiting lipotoxicity and HIF1α pathways.

The consequences of a high-calorie diet background before calorie restriction on skeletal muscles in a mouse model

The beneficial effects of calorie restriction (CR) are numerous. However, there is no scientific evidence about how a high-calorie diet (HCD) background influences the mechanisms underlying CR on skeletal muscles in an experimental mouse model. Herein we present empirical evidence showing significant interactions between HCD (4 months) and CR (3 months). Pectoralis major and quadriceps femoris vastus medialis, in the experimental and control groups, displayed metabolic and physiologic heterogeneity and remarkable plasticity, according to the dietary interventions. HCD-CR not only altered genetic activation patterns of satellite SC markers but also boosted the expression of myogenic regulatory factors and key activators of mitochondrial biogenesis, which in turn were also associated with metabolic fiber transition. Our data prompt us to theorize that the effects of CR may vary according to the physiologic, metabolic, and genetic peculiarities of the skeletal muscle described here and that INTM/IM lipid infiltration and tissue-specific fuel-energy status (demand/supply) both hold dependent-interacting roles with other key anti-aging mechanisms triggered by CR. Systematic integration of an HCD with CR appears to bring potential benefits for skeletal muscle function and energy metabolism. However, at this stage of our research, an optimal balance between the two dietary conditions, where anti-aging effects can be accomplished, is under intensive investigation in combination with other tissues and organs at different levels of organization within the organ system.

Flavonoids as antiobesity agents: A review

Obesity is a global health problem that affects all age groups in both developing and developed countries. In recent years, the prevalence of overweight and obesity has reached pandemic levels, resulting in a dramatic increase in the incidence of various comorbidities, such as cardiovascular diseases, type 2 diabetes, and cancer, consequently leading to massive health and socioeconomic burdens. Together with lifestyle changes, antiobesity pharmacotherapy is gaining momentum as an adjunctive treatment. However, the available pharmacological approaches have limited use owing to either significant adverse effects or low efficacy. Over the years, natural products have been an important source of lead compounds for drug discovery. Among these, flavonoids are associated with important biological effects and health-promoting activities. In this review, we discuss the modulatory effects of flavonoids on obesity and their potential mechanisms of action. The literature strongly suggests that most common flavonoids demonstrate a pronounced effect on obesity as shown by their ability to lower body weight, fat mass, and plasma triglycerides/cholesterol, both in in vitro and in vivo models. The impact of flavonoids on obesity can be observed through different mechanisms: reducing food intake and fat absorption, increasing energy expenditure, modulating lipid metabolism, or regulating gut microbiota profile. A better understanding of the known antiobesity mechanisms of flavonoids will enable their potential use to treat this medical condition. Therefore, this review focuses on the putative biological mechanisms through which flavonoids may prevent or treat obesity and highlights new perspectives on future pharmacological use.

Soluble Epoxide Hydrolase Inhibition by t-TUCB Promotes Brown Adipogenesis and Reduces Serum Triglycerides in Diet-Induced Obesity

Brown adipose tissue (BAT) is an important target for obesity treatment and prevention. Soluble epoxide hydrolase (sEH) converts bioactive epoxy fatty acids (EpFAs) into less active diols. sEH inhibitors (sEHI) are beneficial in many chronic diseases by stabilizing EpFAs. However, roles of sEH and sEHI in brown adipogenesis and BAT activity in treating diet-induced obesity (DIO) have not been reported. sEH expression was studied in in vitro models of brown adipogenesis and the fat tissues of DIO mice. The effects of the sEHI, trans-4-{4-[3-(4-trifluoromethoxy-phenyl)-ureido]-cyclohexyloxy-benzoic acid (t-TUCB), were studied in vitro and in the obese mice via mini osmotic pump delivery. sEH expression was increased in brown adipogenesis and the BAT of the DIO mice. t-TUCB promoted brown adipogenesis in vitro. Although t-TCUB did not change body weight, fat pad weight, or glucose and insulin tolerance in the obese mice, it decreased serum triglycerides and increased protein expression of genes important for lipid metabolism in the BAT. Our results suggest that sEH may play a critical role in brown adipogenesis, and sEHI may be beneficial in improving BAT protein expression involved in lipid metabolism. Further studies using the sEHI combined with EpFA generating diets for obesity treatment and prevention are warranted.

Pasteurized Akkermansia muciniphila increases whole-body energy expenditure and fecal energy excretion in diet-induced obese mice

Accumulating evidence points to Akkermansia muciniphila as a novel candidate to prevent or treat obesity-related metabolic disorders. We recently observed, in mice and in humans, that pasteurization of A. muciniphila increases its beneficial effects on metabolism. However, it is currently unknown if the observed beneficial effects on body weight and fat mass gain are due to specific changes in energy expenditure. Therefore, we investigated the effects of pasteurized A. muciniphila on whole-body energy metabolism during high-fat diet feeding by using metabolic chambers. We confirmed that daily oral administration of pasteurized A. muciniphila alleviated diet-induced obesity and decreased food energy efficiency. We found that this effect was associated with an increase in energy expenditure and spontaneous physical activity. Strikingly, we discovered that energy expenditure was enhanced independently from changes in markers of thermogenesis or beiging of the white adipose tissue. However, we found in brown and white adipose tissues that perilipin2, a factor associated with lipid droplet and known to be altered in obesity, was decreased in expression by pasteurized A. muciniphila. Finally, we observed that treatment with pasteurized A. muciniphila increased energy excretion in the feces. Interestingly, we demonstrated that this effect was not due to the modulation of intestinal lipid absorption or chylomicron synthesis but likely involved a reduction of carbohydrates absorption and enhanced intestinal epithelial turnover. In conclusion, this study further dissects the mechanisms by which pasteurized A. muciniphila reduces body weight and fat mass gain. These data also further support the impact of targeting the gut microbiota by using specific bacteria to control whole-body energy metabolism.

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

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

Childhood Obesity Risk in Relationship to Perilipin 1 (PLIN1) Gene Regulation by Circulating microRNAs

Childhood obesity is a growing public health burden in many countries. The lipid perilipin 1 (PLIN1) gene is involved in regulation of lipolysis, and thus represents a viable candidate mechanism for obesity genetics research in children. In addition, the regulation of candidate gene expression by circulating microRNAs (miRNAs) offers a new research venue for diagnostic innovation. We report new findings on associations among circulating miRNAs, regulation of the PLIN1 gene, and susceptibility to childhood obesity. In a sample of 135 unrelated subjects, 35 children with obesity (between ages 3 and 13) and 100 healthy controls (between ages 4 and 16), we examined the expression levels of four candidate miRNAs (hsa-miR-4777-3p, hsa-miR-642b-3p, hsa-miR-3671-1, and hsa-miR-551b-2) targeting the PLIN1 as measured by real-time polymerase chain reaction in whole blood samples. We found that the full genetic model, including the four candidate miRNAs and the PLIN1 gene, explained a statistically significant 12.7% of the variance in childhood obesity risk (p = 0.0034). The four miRNAs together explained 10.1% of the risk (p = 0.008). The percentage of variation in childhood obesity risk explained by hsa-miR-642b-3p and age was 19%. In accordance with biological polarity of the observed association, for example, hsa-miR-642b-3p was upregulated, while the PLIN1 expression decreased in obese participants compared to healthy controls. To the best of our knowledge, this is the first clinical association study of these candidate miRNAs targeting the PLIN1 in childhood obesity. These data offer new molecular leads for future clinical biomarker and diagnostic discovery for childhood obesity.

Mechanistic Links Between Obesity, Diabetes, and Blood Pressure: Role of Perivascular Adipose Tissue

Obesity is increasingly prevalent and is associated with substantial cardiovascular risk. Adipose tissue distribution and morphology play a key role in determining the degree of adverse effects, and a key factor in the disease process appears to be the inflammatory cell population in adipose tissue. Healthy adipose tissue secretes a number of vasoactive adipokines and anti-inflammatory cytokines, and changes to this secretory profile will contribute to pathogenesis in obesity. In this review, we discuss the links between adipokine dysregulation and the development of hypertension and diabetes and explore the potential for manipulating adipose tissue morphology and its immune cell population to improve cardiovascular health in obesity.

Effects of caloric restriction on the expression of lipocalin-2 and its receptor in the brown adipose tissue of high-fat diet-fed mice

Obesity causes inflammation and impairs thermogenic functions in brown adipose tissue (BAT). The adipokine lipocalin 2 (LCN2) has been implicated in inflammation and obesity. Herein, we investigated the protective effects of caloric restriction (CR) on LCN2-mediated inflammation and oxidative stress in the BAT of high-fat diet (HFD)-fed mice. Mice were fed a HFD for 20 weeks and then either continued on the HFD or subjected to CR for the next 12 weeks. CR led to the browning of the white fat-like phenotype in HFD-fed mice. Increased expressions of LCN2 and its receptor in the BAT of HFD-fed mice were significantly attenuated by CR. Additionally, HFD+CR-fed mice had fewer neutrophils and macrophages expressing LCN2 and iron-positive cells than HFD-fed mice. Further, oxidative stress and mitochondrial fission induced by a HFD were also significantly attenuated by CR. Our findings indicate that the protective effects of CR on inflammation and oxidative stress in the BAT of obese mice may be associated with regulation of LCN2.

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.

The data of change in macrophage gene expression which induced by perilipin 1 overexpression

The data presented here are related to the research article entitled “Overexpression of Perilipin1 protects against atheroma progression in apolipoprotein E knockout mice” [1]. This paper describes data that were obtained from perilipin 1 (PLIN1) transgenic mice (Plin1Tg) regarding atherosclerosis. The main aim of collecting the data was to clarify the role of PLIN1 in the pathophysiology of atherosclerosis. The data were collected from C57BL/6J mice, apolipoprotein E knockout mice (ApoeKO) and Plin1Tg/ApoeKO. The atherosclerotic lesion areas of aorta were 3.3 ± 1.2% in C57BL/6J mice, 14.2 ± 3.2% in ApoeKO, and 5.6 ± 1.9% in Plin1Tg/ApoeKO. Body weight, gonadal adipose mass and plasma triglyceride concentrations were comparable among the three groups [1]. Furthermore, PLIN1 overexpression did not affect the gene expressions related to cholesterol influx and efflux in macrophage.

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.

Perilipin 3 Deficiency Stimulates Thermogenic Beige Adipocytes Through PPARα Activation

Beige adipocytes can dissipate energy as heat. Elaborate communication between metabolism and gene expression is important in the regulation of beige adipocytes. Although lipid droplet (LD) binding proteins play important roles in adipose tissue biology, it remains unknown whether perilipin 3 (Plin3) is involved in the regulation of beige adipocyte formation and thermogenic activities. In this study, we demonstrate that Plin3 ablation stimulates beige adipocytes and thermogenic gene expression in inguinal white adipose tissue (iWAT). Compared with wild-type mice, Plin3 knockout mice were cold tolerant and displayed enhanced basal and stimulated lipolysis in iWAT, inducing peroxisome proliferator-activated receptor α (PPARα) activation. In adipocytes, Plin3 deficiency promoted PPARα target gene and uncoupling protein 1 expression and multilocular LD formation upon cold stimulus. Moreover, fibroblast growth factor 21 expression and secretion were upregulated, which was attributable to activated PPARα in Plin3-deficient adipocytes. These data suggest that Plin3 acts as an intrinsic protective factor preventing futile beige adipocyte formation by limiting lipid metabolism and thermogenic gene expression.

Overexpression of perilipin1 protects against atheroma progression in apolipoprotein E knockout mice

BACKGROUND AND AIMS

Perilipin1 (PLIN1), a lipid droplet-associated protein, plays an important role in the regulation of lipolysis and lipid storage in adipocytes. PLIN1 has recently been reported to be expressed in macrophages within atheroma plaques, suggesting PLIN1 may play a role in the accumulation of lipids at the arterial wall and in the development of atherosclerosis. To clarify the role of PLIN1 in the pathophysiology of atherosclerosis, we assessed the progression of atherosclerosis in PLIN1 transgenic mice (Plin1Tg).

METHODS

Plin1Tg were crossed with apolipoprotein E knockout mice (ApoeKO). C57BL/6J mice, ApoeKO and Plin1Tg/ApoeKO received a normal chow diet for 20 weeks. Body weight, gonadal fat mass and plasma lipid concentrations were measured. Aortas were collected for quantification of atheroma lesions and histological analysis by Oil Red O staining.

RESULTS

Body weight, gonadal adipose mass and plasma triglyceride concentrations were not significantly different among the three groups. In contrast, the atherosclerotic lesion area was significantly increased in ApoeKO (14.2 ± 3.2%; p < .01) compared with C57BL/6J mice (3.3 ± 1.2%) and Plin1Tg/ApoeKO (5.6 ± 1.9%).

CONCLUSIONS

Overexpressed PLIN1 in macrophages had a protected role against atheroma progression in ApoeKO in the absence of changes in gonadal fat mass or plasma lipid levels, presumably due to modification of the stability and/or inflammatory profile of macrophages.

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.

Haematopoietic TLR4 deletion attenuates perivascular brown adipose tissue inflammation in atherosclerotic mice

AIMS

To investigate whether haematopoietic TLR4 deletion attenuates perivascular brown adipose tissue inflammation in atherosclerotic mice.

METHODS AND RESULTS

Experiments were performed using irradiated LDL receptor-deficient (LDLR^-/-) mice with marrow from either TLR4-deficient (TLR4^-/-) or age-matched wild-type (WT) mice. After 12 weeks of being fed a high-cholesterol diet, TLR4^-/-→LDLR^-/- mice developed fewer atherosclerotic lesions in the aorta compared to WT→LDLR^-/- mice. This effect was associated with an increase in multilocular lipid droplets and mitochondria in perivascular adipose tissue (PVAT). Immunofluorescence analysis confirmed that there was an increase in capillary density and M2 macrophage infiltration, accompanied by a decrease in tumour necrosis factor (TNF)-α expression in the localized PVAT of TLR4^-/-→LDLR^-/- mice. In vitro studies indicated that bone marrow-derived macrophages (BMDMs) from WT mice demonstrated an M1-like phenotype and expression of inflammatory cytokines induced by palmitate. These effects were attenuated in BMDMs isolated from TLR4^-/- mice. Furthermore, brown adipocytes incubated with conditioned medium (CM) derived from palmitate-treated BMDMs, exhibited larger and more unilocular lipid droplets, and reduced expression of brown adipocyte-specific markers and perilipin-1 compared to those observed in brown adipocytes exposed to CM from palmitate-treated BMDMs of TLR4^-/- mice. This decreased potency was primarily due to TNF-α, as demonstrated by the capacity of the TNF-α neutralizing antibody to reverse these effects.

CONCLUSIONS

These results suggest that haematopoietic-specific deletion of TLR4 promotes PVAT homeostasis, which is involved in reducing macrophage-induced TNF-α secretion and increasing mitochondrial biogenesis in brown adipocytes.

The effects of detraining and training on adipose tissue lipid droplet in obese mice after chronic high-fat diet

Background

It is well known that exercise promotes lipolysis by stimulating the lipid droplet (LD) signaling pathway. However, few studies have been conducted to examine the effect of detraining with high fat diet (HFD) and training effects after long-term HFD. Here, we investigated the effect of detraining and training on adipose tissue LD pathway in diet-induced obese mice after continuous HFD.

Methods

Seventy male C57BL/6 mice were randomly assigned into a Normal diet + Sedentary group (ND, n = 10) or a High-fat diet + Sedentary group (HF, n = 50); in the HF group, obesity was induced by a 45% fat chow for six weeks. For the subsequent eight weeks, the HF group was randomly subdivided into an HF (n = 30) or an HF + training group (HFT, n = 20), and the HFT group was subjected to treadmill training while on an HFD. Following this eight-week period, the HFT group stopped exercising (HFT-DT group, n = 10), and the mice in the HF group were randomly subdivided into an HF (n = 10) or an HF + training group (HF-T, n = 10). After training and detraining, abdominal visceral fat was obtained and analyzed by histological staining and western blot.

Results

Treadmill exercise decreased body weight and fat mass (P <0.05), and increased the levels of PKA, perilipin1, CGI-58, ATGL, and HSL (P <0.05) after eight weeks of training. Following eight weeks of detraining, the levels of PKA and HSL were decreased (P <0.05); however, exercise after chronic HFD increased the levels of PKA, perilipin1, CGI-58, ATGL, and HSL (P <0.05), and decreased body weight and fat mass (P <0.05).

Conclusions

Regardless of dietary restrictions, exercise is an effective treatment for obesity, owing to the regulation of LD signaling proteins. Moreover, the effects of regular exercise after chronic HFD were similar to those of exercise in the absence of HFD. Therefore, although obesity is induced by chronic HFD, exercise without dietary change is sufficiently effective for obesity treatment regardless of the preceding HFD period.

Perilipin 2 and Age-Related Metabolic Diseases: A New Perspective

Perilipin 2 (Plin2), a protein associated with the metabolism of intracellular lipid droplets (LDs), has long been considered only for its role in lipid storage. However, the manipulation of its expression affects the severity of a variety of metabolic and age-related diseases, such as fatty liver, insulin resistance and type 2 diabetes (T2D), cardiovascular disease, atherosclerosis, sarcopenia, and cancer, suggesting that this protein may play a role in these pathological conditions. In particular, its downregulation in mice prevents or mitigates some of the above mentioned diseases. Conversely, in humans high levels of Plin2 are present in sarcopenia, hepatic steatosis, atherosclerosis, and some types of cancer. We propose that inhibition of Plin2 might be a strategy to counteract several metabolic and age-related diseases.

Systemic Chromosome Instability Resulted in Colonic Transcriptomic Changes in Metabolic, Proliferation, and Stem Cell Regulators in Sgo1-/+ Mice

Colon cancer is the second most lethal cancer and is predicted to claim 49,700 lives in the United States this year. Chromosome instability (CIN) is observed in 80% to 90% of colon cancers and is thought to contribute to colon cancer progression and recurrence. To investigate the impact of CIN on colon cancer development, we developed shugoshin-1 (Sgo1) haploinsufficient (-/+) mice, an animal model focusing on mitotic error-induced CIN. In this study, we analyzed signature changes in the colonic transcriptome of Sgo1(-/+) mice to examine the molecular events underlying the altered carcinogenesis profiles in Sgo1(-/+) mice. We performed next-generation sequencing of normal-looking colonic mucosal tissue from mice treated with the carcinogen azoxymethane after 24 weeks. Transcriptome profiling revealed 349 hits with a 2-fold expression difference threshold (217 upregulated genes, 132 downregulated genes, P < 0.05). Pathway analyses indicated that the Sgo1-CIN tissues upregulated pathways known to be activated in colon cancer, including lipid metabolism (z score 4.47), Notch signaling (4.47), insulin signaling (3.81), and PPAR pathways (3.75), and downregulated pathways involved in immune responses including allograft rejection (6.69) and graft-versus-host disease (6.54). Notably, stem cell markers were also misregulated. Collectively, our findings demonstrate that systemic CIN results in transcriptomic changes in metabolism, proliferation, cell fate, and immune responses in the colon, which may foster a microenvironment amenable to cancer development. Therefore, therapeutic approaches focusing on these identified pathways may be valuable for colon cancer prevention and treatment.

Chrysin induces brown fat-like phenotype and enhances lipid metabolism in 3T3-L1 adipocytes

OBJECTIVES

Many studies have to do with promising therapeutic phytochemicals such as flavonoids to treat obesity and related complications, and a number of dietary compounds have been proposed as tools for increasing energy expenditure and decreasing fat accumulation in mammals. Here, we show that the flavonoid chrysin induces browning of 3T3-L1 adipocytes via enhanced expression of brown fat-specific genes and proteins as well as enhances lipid metabolism.

METHODS

Chrysin-induced fat browning was investigated by determining expression levels of brown fat-specific genes and proteins by real-time polymerase chain reaction and immunoblot analysis, respectively.

RESULTS

Chrysin enhanced expression of brown fat-specific markers and increased protein levels of peroxisome proliferator-activated receptor (PPAR)α, PPARγ, PPARδ, phosphorylated AMP-activated protein kinase (p-AMPK), phosphorylated acetyl-CoA carboxylase, hormone sensitive lipase, perilipin, carnitine palmitoyltransferase 1, acyl-coenzyme A oxidase 1, peroxisome proliferator-activated receptor-1 alpha (PGC-1α), and uncoupling protein 1 (UCP-1), suggesting its possible role in augmentation of lipolysis, fat oxidation, and thermogenesis as well as reduction of lipogenesis. Increased expression of UCP-1 and other brown fat-specific markers was possibly mediated by chrysin-induced activation of AMPK based on the fact that inhibition of AMPK by dorsomorphin abolished expression of PR domain-containing 16, UCP-1, and PGC-1α while the activator 5-aminoimidazole-4-carboxamide ribonucleotide elevated expression of these brown marker proteins.

CONCLUSION

Our findings suggest that chrysin plays a dual modulatory role in the form of inducing the brown-like phenotype as well as enhancing lipid metabolism and thus may be explored as a potentially promising food additive for prevention of obesity.

Obesity-associated sympathetic overactivity in children and adolescents: the role of catecholamine resistance in lipid metabolism

BACKGROUND

Obesity in children and adolescents is characterized by chronic sympathetic overdrive and reduced epinephrine-stimulated lipolysis. This resistance to catecholamines occurs during the dynamic phase of fat accumulation. This review will focus on the relationship between sympathetic-adrenal activity and lipid metabolism, thereby highlighting the role of catecholamine resistance in the development of childhood obesity.

RESULTS AND CONCLUSIONS

Catecholamine resistance causes lipid accumulation in adipose tissue by reducing lipolysis, increasing lipogenesis and impeding free fatty acid (FFA) transportation. Exercise improves catecholamine resistance, as evidenced by attenuated systemic sympathetic activity, reduced circulating catecholamine levels and enhanced β-adrenergic receptor signaling. Insulin resistance is mostly a casual result rather than a cause of childhood obesity. Therefore, catecholamine resistance in childhood obesity may promote insulin signaling in adipose tissue, thereby increasing lipogenesis. This review outlines a series of evidence for the role of catecholamine resistance as an upstream mechanism leading to childhood obesity.

Lipolysis and lipases in white adipose tissue - An update

Lipolysis is defined as the sequential hydrolysis of triacylglycerol (TAG) stored in cell lipid droplets. For many years, it was believed that hormone-sensitive lipase (HSL) and monoacylglycerol lipase (MGL) were the main enzymes catalyzing lipolysis in the white adipose tissue. Since the discovery of adipose triglyceride lipase (ATGL) in 2004, many studies were performed to investigate and characterize the actions of this lipase, as well as of other proteins and possible regulatory mechanisms involved, which reformulated the concept of lipolysis. Novel findings from these studies include the identification of lipolytic products as signaling molecules regulating important metabolic processes in many non-adipose tissues, unveiling a previously underestimated aspect of lipolysis. Thus, we present here an updated review of concepts and regulation of white adipocyte lipolysis with a special emphasis in its role in metabolism homeostasis and as a source of important signaling molecules.

Pathways commonly dysregulated in mouse and human obese adipose tissue: FAT/CD36 modulates differentiation and lipogenesis

Obesity is linked to adipose tissue hypertrophy (increased adipocyte cell size) and hyperplasia (increased cell number). Comparative analyses of gene datasets allowed us to identify 1426 genes which may represent common adipose phenotype in humans and mice. Among them we identified several adipocyte-specific genes dysregulated in obese adipose tissue, involved in either fatty acid storage (acyl CoA synthase ACSL1, hormone-sensitive lipase LIPE, aquaporin 7 AQP7, perilipin PLIN) or cell adhesion (fibronectin FN1, collagens COL1A1, COL1A3, metalloprotein MMP9, or both (scavenger receptor FAT/CD36). Using real-time analysis of cell surface occupancy on xCELLigence system we developed a new method to study lipid uptake and differentiation of mouse 3T3L1 fibroblasts and human adipose stem cells. Both processes are regulated by insulin and fatty acids such as oleic acid. We showed that fatty acid addition to culture media increased the differentiation rate and was required for full differentiation into unilocular adipocytes. Significant activation of lipogenesis, i.e. lipid accumulation, by either insulin or oleic acid was monitored in times ranging from 1 to 24 h, depending on differentiation state, whereas significant effects on adipogenesis, i.e., surperimposed lipid accumulation and gene transcriptional regulations were measured after 3 to 4 d. Combination of selected times for analysis of lipid contents, cell counts, size fractionations, and gene transcriptional regulations showed that FAT/CD36 specific inhibitor AP5258 significantly increased cell survival of oleic acid-treated mouse and human adipocytes, and partially restored the transcriptional response to oleic acid in the presence of insulin through JNK pathway. Taken together, these data open new perspectives to study the molecular mechanisms commonly dysregulated in mouse and human obesity at the level of lipogenesis linked to hypertrophy and adipogenesis linked to hyperplasia.

Molecular pathways regulating the formation of brown-like adipocytes in white adipose tissue

Adipose tissue is functionally composed of brown adipose tissue and white adipose tissue. The unique thermogenic capacity of brown adipose tissue results from expression of uncoupling protein 1 in the mitochondrial inner membrane. On the basis of recent findings that adult humans have functionally active brown adipose tissue, it is now recognized as playing a much more important role in human metabolism than was previously thought. More importantly, brown-like adipocytes can be recruited in white adipose tissue upon environmental stimulation and pharmacologic treatment, and this change is associated with increased energy expenditure, contributing to a lean and healthy phenotype. Thus, the promotion of brown-like adipocyte development in white adipose tissue offers novel possibilities for the development of therapeutic strategies to combat obesity and related metabolic diseases. In this review, we summarize recent advances in understanding the molecular mechanisms involved in the recruitment of brown-like adipocyte in white adipose tissue.

Similar and additive effects of ovariectomy and diabetes on insulin resistance and lipid metabolism

Type 2 diabetes mellitus (T2DM) is among the leading causes of death in postmenopausal women. The disruption of ovarian function may contribute to the incidence of T2DM. The purpose of this study was to investigate the effects of ovariectomy and T2DM on glucose and lipid homeostasis, perilipin levels in adipose tissues, as a lipolytic regulator, and levels of certain adipokines. Ovariectomized (OVX) rats were used as a model for postmenopausal women. The study was performed on sham, OVX, sham diabetic, and OVX diabetic female rats. The results indicated that ovariectomy alters adipose tissue metabolism through reducing perilipin content in white adipose tissue (WAT); however it has no effect on perilipin level in brown adipose tissue (BAT). OVX diabetic females suffer from serious metabolic disturbances, suggested by exacerbation of insulin resistance in terms of disrupted lipid profile, higher HOMA-IR, hyperinsulinemia, higher leptin, and lower adiponectin concentrations. These metabolic derangements may underlie the predisposition for cardiovascular disease in women after menopause. Therefore, for efficient treatment, the menopausal status of diabetic female should be addressed, and the order of events is of great importance because ovariectomy following development of diabetes has more serious complications compared to development of diabetes as result of menopause.

White, brite, and brown adipocytes: the evolution and function of a heater organ in mammals

Brown fat is a specialized heater organ in eutherian mammals. In contrast to the energy storage function of white adipocytes, brown adipocytes dissipate nutrient energy by uncoupling of mitochondrial oxidative phosphorylation, which depends on uncoupling protein 1 (UCP1). UCP1, as well as UCP2 and UCP3, belong to the family of mitochondrial carriers inserted into the inner mitochondrial membrane for metabolite trafficking between the matrix and the intermembrane space. UCP1 transports protons into the mitochondrial matrix when activated by a rise in free fatty acid levels in the cell. This UCP1-dependant proton leak drives high oxygen consumption rates in the absence of ATP synthesis and dissipates proton motive force as heat. The enormous heating capacity of brown fat is supported by dense vascularization, high rates of tissue perfusion, and high mitochondrial density in brown adipocytes.

It has been known for more than 50 years that nonshivering thermogenesis in brown fat serves to maintain body temperature of neonates and small mammals in cold environments, and is used by hibernators for arousal from torpor. It has been speculated that the development of brown fat as a new source for nonshivering thermogenesis provided mammals with a unique advantage for survival in the cold. Indeed brown fat and UCP1 is found in ancient groups of mammals, like the afrotherians and marsupials. In the latter, however, the thermogenic function of UCP1 and brown fat has not been demonstrated as of yet. Notably, orthologs of all three mammalian UCP genes are also present in the genomes of bony fishes and in amphibians. Molecular phylogeny reveals a striking increase in the substitution rate of UCP1 between marsupial and eutherian lineages. At present, it seems that UCP1 only gained thermogenic function in brown adipocytes of eutherian mammals, whereas the function of UCP1 and that of the other UCPs in ectotherms remains to be identified.

Evolution of thermogenic function required expression of UCP1 in a brown-adipocyte-like cell equipped with high mitochondrial density embedded in a well-vascularized tissue. Brown-adipocyte-like cells in white adipose tissue, called “brite” (brown-in-white) or “beige” adipocytes, emerge during adipogenesis and in response to cold exposure in anatomically distinct adipose tissue depots of juvenile and adult rodents. These brite adipocytes may resemble the archetypical brown adipocyte in vertebrate evolution. It is therefore of interest to elucidate the molecular mechanisms of brite adipocyte differentiation, study the bioenergetic properties of these cells, and search for the presence of related brown-adipocyte-like cells in nonmammalian vertebrates.

Regulation of adipocyte lipolysis

In adipocytes the hydrolysis of TAG to produce fatty acids and glycerol under fasting conditions or times of elevated energy demands is tightly regulated by neuroendocrine signals, resulting in the activation of lipolytic enzymes. Among the classic regulators of lipolysis, adrenergic stimulation and the insulin-mediated control of lipid mobilisation are the best known. Initially, hormone-sensitive lipase (HSL) was thought to be the rate-limiting enzyme of the first lipolytic step, while we now know that adipocyte TAG lipase is the key enzyme for lipolysis initiation. Pivotal, previously unsuspected components have also been identified at the protective interface of the lipid droplet surface and in the signalling pathways that control lipolysis. Perilipin, comparative gene identification-58 (CGI-58) and other proteins of the lipid droplet surface are currently known to be key regulators of the lipolytic machinery, protecting or exposing the TAG core of the droplet to lipases. The neuroendocrine control of lipolysis is prototypically exerted by catecholaminergic stimulation and insulin-induced suppression, both of which affect cyclic AMP levels and hence the protein kinase A-mediated phosphorylation of HSL and perilipin. Interestingly, in recent decades adipose tissue has been shown to secrete a large number of adipokines, which exert direct effects on lipolysis, while adipocytes reportedly express a wide range of receptors for signals involved in lipid mobilisation. Recently recognised mediators of lipolysis include some adipokines, structural membrane proteins, atrial natriuretic peptides, AMP-activated protein kinase and mitogen-activated protein kinase. Lipolysis needs to be reanalysed from the broader perspective of its specific physiological or pathological context since basal or stimulated lipolytic rates occur under diverse conditions and by different mechanisms.

Brown fat fuel utilization and thermogenesis

Brown adipose tissue (BAT) dissipates energy as heat to maintain optimal thermogenesis and to contribute to energy expenditure in rodents and possibly humans. The energetic processes executed by BAT require a readily-available fuel supply, which includes glucose and fatty acids (FAs). FAs become available by cellular uptake, de novo lipogenesis, and multilocular lipid droplets in brown adipocytes. BAT also possesses a great capacity for glucose uptake and metabolism, and an ability to regulate insulin sensitivity. These properties make BAT an appealing target for the treatment of obesity, diabetes, and other metabolic disorders. Recent research has provided a better understanding of the processes of fuel utilization carried out by brown adipocytes, which is the focus of the current review.

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

Biochemical and cell-based studies have identified the G0S2 (G0/G1 switch gene 2) as a selective inhibitor of the key intracellular triacylglycerol hydrolase, adipose triglyceride lipase. To better understand the physiological role of G0S2, we constructed an adipose tissue-specific G0S2 transgenic mouse model. In comparison with wild type animals, the transgenic mice exhibited a significant increase in overall fat mass and a decrease in peripheral triglyceride accumulation. Basal and adrenergically stimulated lipolysis was attenuated in adipose explants isolated from the transgenic mice. Following fasting or injection of a β3-adrenergic agonist, in vivo lipolysis and ketogenesis were decreased in G0S2 transgenic mice when compared with wild type animals. Consequently, adipose overexpression of G0S2 prevented the "switch" of energy substrate from carbohydrates to fatty acids during fasting. Moreover, G0S2 overexpression promoted accumulation of more and larger lipid droplets in brown adipocytes without impacting either mitochondrial morphology or expression of oxidative genes. This phenotypic change was accompanied by defective cold adaptation. Furthermore, feeding with a high fat diet caused a greater gain of both body weight and adiposity in the transgenic mice. The transgenic mice also displayed a decrease in fasting plasma levels of free fatty acid, triglyceride, and insulin as well as improved glucose and insulin tolerance. Cumulatively, these results indicate that fat-specific G0S2 overexpression uncouples adiposity from insulin sensitivity and overall metabolic health through inhibiting adipose lipolysis and decreasing circulating fatty acids.