Depot-specific regulation of perilipin by rosiglitazone in a diabetic animal model

Perilipin 2 Protects against Lipotoxicity-Induced Islet Fibrosis by Inducing Islet Stellate Cell Activation Phenotype Changes

Aims

We explored whether and how perilipin 2 (Plin2) protected islets against lipotoxicity-induced islet dysfunction by regulating islet stellate cells (ISCs) activation.

Methods

Six-week-old male rats were given a high-fat diet or a control diet for 28 weeks. Glucose metabolic phenotypes were assessed using glucose/insulin tolerance tests, masson, and immunohistochemical staining. ISCs activation levels were assessed from rats and palmitic acid- (PA-) treated cultured ISCs by immunofluorescence, Oil red O staining, electron microscopy, quantitative PCR, and western blotting. Changes in ISCs phenotype of activation degree and its underlying mechanisms were assessed by target gene lentiviral infection, high-performance liquid chromatography (HPLC), and western blotting.

Results

Obese rats showed glucose intolerance, decreased endocrine hormone profiles, and elevated expression of α-smooth muscle actin (α-SMA), a polygonal appearance without cytoplasmic lipid droplets of ISCs in rats and isolated islets. PA-treated cultured ISCs exhibited faster proliferation and migration abilities with the induction of mRNA levels of lipid metabolism proteins, especially Plin2. The overexpression of Plin2 resulted in ISCs “re-quiescent” phenotypes associated with inhibition of the Smad3-TGF-β signaling pathways.

Conclusions

Our observations suggest a protective role of Plin2 in weakening ISCs activation. It may serve as a novel therapeutic target for preventing islet fibrosis for T2DM.

Role of CaMKII in the regulation of fatty acids and lipid metabolism

BACKGROUND & AIMS

Previous studies have reported the beneficial roles of the activation of calmodulin-dependent protein kinase (CaMK)II to many cellular functions associated with human health. This review aims at discussing its activation by exercise as well as its roles in the regulation of unsaturated, saturated, omega 3 fatty acids, and lipid metabolism.

METHODS

A wide literature search was conducted using online database such as 'PubMed', 'Google Scholar', 'Researcher', 'Scopus' and the website of World Health Organization (WHO) as well as Control Disease and Prevention (CDC). The criteria for the search were mainly lipid and fatty acid metabolism, diabetes, and metabolic syndrome (MetS). A total of ninety-seven articles were included in the review.

RESULTS

Calmodulin-dependent protein kinase activation by exercise is helpful in controlling membrane lipids related with type 2 diabetes and obesity. CaMKII regulates many health beneficial cellular functions in individuals who exercise compared with those who do not exercise. Regulation of lipid metabolism and fatty acids are crucial in the improvement of metabolic syndrome.

CONCLUSIONS

Approaches that involve CaMKII could be a new avenue for designing novel and effective therapeutic modalities in the treatment or better management of metabolic diseases such as type 2 diabetes and obesity.

Lipid metabolism in inflammation-related diseases

There are thousands of lipid species existing in cells, which belong to eight different categories. Lipids are the essential building blocks of cells. Recent studies have started to unveil the important functions of lipids in regulating cell metabolism. However, we are still at a very early stage in fully understanding the physiological and pathological functions of lipids. The application of lipidomics for studying lipid metabolism can provide a direct readout of the cellular status and broadens our understanding of the mechanisms that underpin metabolic disease states. This review provides an introduction to lipid metabolism and its role in modulating homeostasis and immunity. We also describe representative applications of lipidomics for studying lipid metabolism in inflammation-related diseases.

Reduction of obesity-associated white adipose tissue inflammation by rosiglitazone is associated with reduced non-alcoholic fatty liver disease in LDLr-deficient mice

Obesity is associated with chronic low-grade inflammation that drives the development of metabolic diseases, including non-alcoholic fatty liver disease (NAFLD). We recently showed that white adipose tissue (WAT) constitutes an important source of inflammatory factors. Hence, interventions that attenuate WAT inflammation may reduce NAFLD development. Male LDLr-/- mice were fed a high-fat diet (HFD) for 9 weeks followed by 7 weeks of HFD with or without rosiglitazone. Effects on WAT inflammation and NAFLD development were analyzed using biochemical and (immuno)histochemical techniques, combined with gene expression analyses. Nine weeks of HFD feeding induced obesity and WAT inflammation, which progressed gradually until the end of the study. Rosiglitazone fully blocked progression of WAT inflammation and activated PPARγ significantly in WAT. Rosiglitazone intervention did not activate PPARγ in liver, but improved liver histology and counteracted the expression of genes associated with severe NAFLD in humans. Rosiglitazone reduced expression of pro-inflammatory factors in WAT (TNF-α, leptin) and increased expression of adiponectin, which was reflected in plasma. Furthermore, rosiglitazone lowered circulating levels of pro-inflammatory saturated fatty acids. Together, these observations provide a rationale for the observed indirect hepatoprotective effects and suggest that WAT represents a promising therapeutic target for the treatment of obesity-associated NAFLD.

Ginsenoside Rb1 ameliorates liver fat accumulation by upregulating perilipin expression in adipose tissue of db/db obese mice

Background

Ginsenoside Rb1 (G-Rb1), the major active constituent of ginseng, improves insulin sensitivity and exerts antidiabetic effects. We tested whether the insulin-sensitizing and antidiabetic effects of G-Rb1 results from a reduction in ectopic fat accumulation, mediated by inhibition of lipolysis in adipocytes.

Methods

Obese and diabetic db/db mice were treated with daily doses of 20 mg/kg G-Rb1 for 14 days. Hepatic fat accumulation was evaluated by measuring liver weight and triglyceride content. Levels of blood glucose and serum insulin were used to evaluate insulin sensitivity in db/db mice. Lipolysis in adipocytes was evaluated by measuring plasma-free fatty acids and glycerol release from 3T3-L1 adipocytes treated with G-Rb1. The expression of relevant genes was analyzed by western blotting, quantitative real-time polymerase chain reaction, and enzyme-linked immunosorbent assay kit.

Results

G-Rb1 increased insulin sensitivity and alleviated hepatic fat accumulation in obese diabetic db/db mice, and these effects were accompanied by reduced liver weight and hepatic triglyceride content. Furthermore, G-Rb1 lowered the levels of free fatty acids in obese mice, which may contribute to a decline in hepatic lipid accumulation. Corresponding to these results, G-Rb1 significantly suppressed lipolysis in 3T3-L1 adipocytes and upregulated the perilipin expression in both 3T3-L1 adipocytes and mouse epididymal fat pads. Moreover, G-Rb1 increased the level of adiponectin and reduced that of tumor necrosis factor-α in obese mice, and these effects were confirmed in 3T3-L1 adipocytes.

Conclusion

G-Rb1 may improve insulin sensitivity in obese and diabetic db/db mice by reducing hepatic fat accumulation and suppressing adipocyte lipolysis; these effects may be mediated via the upregulation of perilipin expression in adipocytes.

Mitochondrial dysfunction induces formation of lipid droplets as a generalized response to stress

Lipid droplet (LD) formation is a hallmark of cellular stress. Cells attempt to combat noxious stimuli by switching their metabolism from oxidative phosphorylation to glycolysis, sparing resources in LDs for generating cellular reducing power and for anabolic biosynthesis. Membrane phospholipids are also a source of LDs. To elucidate the formation of LDs, we exposed mice to hyperoxia, hypoxia, myocardial ischemia, and sepsis induced by cecal ligation and puncture (CLP). All the above-mentioned stressors enhanced the formation of LDs, as assessed by transmission electron microscopy, with severe mitochondrial swelling. Disruption of mitochondria by depleting mitochondrial DNA ( ρ 0 cells) significantly augmented the formation of LDs, causing transcriptional activation of fatty acid biosynthesis and metabolic reprogramming to glycolysis. Heme oxygenase (HO)-1 counteracts CLP-mediated septic shock in mouse models. In HO-1-deficient mice, LD formation was not observed upon CLP, but a concomitant decrease in "LD-decorating proteins" was observed, implying a link between LDs and cytoprotective activity. Collectively, LD biogenesis during stress can trigger adaptive LD formation, which is dependent on mitochondrial integrity and HO-1 activity; this may be a cellular survival strategy, apportioning energy-generating substrates to cellular defense.

Modulation of the transcriptional activity of peroxisome proliferator-activated receptor gamma by protein-protein interactions and post-translational modifications

Peroxisome proliferator-activated receptor gamma (PPARγ) belongs to a nuclear receptor superfamily; members of which play key roles in the control of body metabolism principally by acting on adipose tissue. Ligands of PPARγ, such as thiazolidinediones, are widely used in the treatment of metabolic syndromes and type 2 diabetes mellitus (T2DM). Although these drugs have potential benefits in the treatment of T2DM, they also cause unwanted side effects. Thus, understanding the molecular mechanisms governing the transcriptional activity of PPARγ is of prime importance in the development of new selective drugs or drugs with fewer side effects. Recent advancements in molecular biology have made it possible to obtain a deeper understanding of the role of PPARγ in body homeostasis. The transcriptional activity of PPARγ is subject to regulation either by interacting proteins or by modification of the protein itself. New interacting partners of PPARγ with new functions are being unveiled. In addition, post-translational modification by various cellular signals contributes to fine-tuning of the transcriptional activities of PPARγ. In this review, we will summarize recent advancements in our understanding of the post-translational modifications of, and proteins interacting with, PPARγ, both of which affect its transcriptional activities in relation to adipogenesis.

Transdifferentiation of MALME-3M and MCF-7 Cells toward Adipocyte-like Cells is Dependent on Clathrin-mediated Endocytosis

Abstract

Enforced cell transdifferentiation of human cancer cells is a promising alternative to conventional chemotherapy. We previously identified albumin-associated lipid- and, more specifically, saturated fatty acid-induced transdifferentiation programs in human cancer cells (HCCLs). In this study, we further characterized the adipocyte-like cells, resulting from the transdifferentiation of human cancer cell lines MCF-7 and MALME-3M, and proposed a common mechanistic approach for these transdifferentiating programs. We showed the loss of pigmentation in MALME-3M cells treated with albumin-associated lipids, based on electron microscopic analysis, and the overexpression of perilipin 2 (PLIN2) by western blotting in MALME-3M and MCF-7 cells treated with unsaturated fatty acids. Comparing the gene expression profiles of naive melanoma MALME-3M cells and albumin-associated lipid-treated cells, based on RNA sequencing, we confirmed the transcriptional upregulation of some key adipogenic gene markers and also an alternative splicing of the adipogenic master regulator PPARG, that is probably related to the reported up regulated expression of the protein. Most importantly, these results also showed the upregulation of genes responsible for Clathrin (CLTC) and other adaptor-related proteins. An increase in CLTC expression in the transdifferentiated cells was confirmed by western blotting. Inactivation of CLTC by chlorpromazine (CHP), an inhibitor of CTLC mediated endocytosis (CME), and gene silencing by siRNAs, partially reversed the accumulation of neutral lipids observed in the transdifferentiated cells. These findings give a deeper insight into the phenotypic changes observed in HCCL to adipocyte-like transdifferentiation and point towards CME as a key pathway in distinct transdifferentiation programs.

Disclosures

Simon C and Aguilar-Gallardo C are co-inventors of the International Patent Application No. PCT/EP2011/004941 entitled “Methods for tumor treatment and adipogenesis differentiation”.

Electronic supplementary material

The online version of this article (doi:10.1186/2193-1801-1-44) contains supplementary material, which is available to authorized users.

Insulin-sensitizing effects on muscle and adipose tissue after dietary fiber intake in men and women with metabolic syndrome

CONTEXT

Dietary fibers have been associated with a reduced incidence of type 2 diabetes mellitus in epidemiological studies; however, the precise mechanisms are unknown.

OBJECTIVE

The objective of the study was to evaluate the efficacy and site of action of an insoluble dietary fiber derived from maize (HAM-RS2) in improving insulin resistance in subjects at increased risk of type 2 diabetes mellitus.

DESIGN

This study was a randomized, controlled crossover, dietary intervention study.

SETTING

The study was conducted at the Centre for Diabetes, Endocrinology, and Research, Royal Surrey County Hospital, Guildford, United Kingdom.

PARTICIPANTS

Fifteen men and women with insulin resistance participated in the study.

INTERVENTION

The intervention included 40 g/d HAM-RS2 compared with a matched placebo for 8 wk.

MAIN OUTCOME MEASURES

After each supplement, participants underwent a two-step hyperinsulinemic-euglycemic clamp study with the addition of glucose tracers; a meal tolerance test; arteriovenous sampling across forearm muscle tissue; and a sc adipose tissue biopsy for assessment of gene expression.

RESULTS

There was enhanced uptake of glucose into the forearm muscle measured by arteriovenous sampling (65 ± 15% increase after resistant starch; P < 0.001). Adipose tissue function was also affected, with enhanced fatty acid suppression after HAM-RS2 treatment and an increase in gene expression for hormone sensitive lipase (P = 0.005), perilipin (P = 0.011), lipoprotein lipase (P = 0.014), and adipose triglyceride lipase (P = 0.03) in biopsy samples. There was no effect on the insulin sensitivity of hepatic glucose production or plasma lipids after HAM-RS2.

CONCLUSION

HAM-RS2 improved peripheral but not hepatic insulin resistance and requires further study as an intervention in patients with or at risk for type 2 diabetes.

Phosphorylated S6K1 (Thr389) is a molecular adipose tissue marker of altered glucose tolerance

Molecular tissue markers of altered glucose metabolism will be useful as potential targets for antidiabetic drugs. S6K1 is a downstream signal of insulin action. We aimed to evaluate (pThr389)S6K1 and total S6K1 levels in human and rat fat depots as candidate markers of altered glucose metabolism. (pThr389)S6K1 and total S6K1 levels were measured using enzyme linked immune sorbent assay (ELISA) in 49 adipose tissue samples from subjects with morbid obesity and in 18 peri-renal white adipose tissue samples from rats. The effects of high glucose and rosiglitazone have been explored in human preadipocytes. (pThr389)S6K1/(total)S6K1 in subcutaneous adipose tissue was significantly increased subjects with Type 2 diabetes (0.78 ± 0.26 vs. 0.55 ± 0.14, P=.02) and associated with fasting glucose (r=0.46, P=.04) and glycated hemoglobin (r=0.63, P=.02) in SAT. Similar associations with fasting glucose (r=0.43, P=.03) and IRS1 (r=-0.41, P=.04) gene expression were found in visceral adipose tissue. In addition, rat experiments confirmed the higher (pThr389)S6K1/totalS6K1 levels in adipose tissue in association with obesity-associated metabolic disturbances. (pThr389)S6K1/totalS6K1 was validated using western blot in rat adipose tissue. Both ELISA and western blot data significantly correlated (r=0.85, P=.005). In human preadipocytes, high glucose medium led to increased (pThr389)S6K1/total S6K1 levels in comparison with normal glucose medium, which was significantly decreased under rosiglitazone administration. In conclusion, in human and rat adipose tissue, phosphorylated S6K1 is a marker for increased glucose levels.

Location, location, location: Beneficial effects of autologous fat transplantation

Visceral adiposity is a risk factor for cardiovascular disorders, type 2 diabetes mellitus (T2D) and associated metabolic diseases. Sub-cutaneous fat is believed to be intrinsically different from visceral fat. To understand molecular mechanisms involved in metabolic advantages of fat transplantation, we studied a rat model of diet-induced adiposity. Adipokine genes (Adiponectin, Leptin, Resistin and Visfatin) were expressed at 10,000 to a million-fold lower in visceral fat depot as compared to peripheral (thigh/chest) fat depots. Interestingly, autologous transplantation of visceral fat to subcutaneous sites resulted in increased gene transcript abundance in the grafts by 3 weeks post-transplantation, indicating the impact of local (residence) factors influencing epigenetic memory. We show here that active transcriptional state of adipokine genes is linked with glucose mediated recruitment of enzymes that regulate histone methylation. Adipose depots have "residence memory" and autologous transplantation of visceral fat to sub-cutaneous sites offers metabolic advantage.

Cloning, structural characterization and expression analysis of a novel lipid storage droplet protein-1 (LSD-1) gene in Chinese honeybee (Apis cerana cerana)

Lipid storage droplet 1 (LSD-1), a PAT family protein located around lipid droplets in insects, is intimately linked to lipid droplets formation and lipid metabolism. Conjugated linoleic acid (CLA) and rosiglitazone (Rosi) have previously been shown to modulate the expression of several PAT family proteins through peroxisome proliferator-activated receptor-γ (PPARγ). In the present study, we isolated and characterized a novel LSD-1 gene, referred to AccLSD-1, from Chinese honeybee (Apis cerana cerana). Sequence analysis indicated that the central region of LSD-1 protein had significant sequence similarity and a typical LSD-1 gene was composed of 8 exons and 7 introns. Interestingly, the first intron of AccLSD-1 including several PPARγ-response elements (PPREs) was located in 5' UTR. Analysis of 5'-flanking region of AccLSD-1 revealed a number of putative cis-acting elements, including three PPREs. Quantitative real-time PCR showed that AccLSD-1 expressed ubiquitously from feeding larva to adult, and its expression level was highest at brown-eyed pupae (Pb) stage. The effect of CLA, Rosi and combination on AccLSD-1 expressions indicated 1% CLA and 0.5 mg/ml Rosi were considered as the suitable diets for rearing adult workers in laboratory, and AccLSD-1 was down-regulated by CLA whereas up-regulated by Rosi. Furthermore, the combination of CLA and Rosi remarkly rescued the suppression of AccLSD-1 expression by CLA alone. These results suggest that AccLSD-1 is associated with A. cerana cerana development, especially during pupal metamorphosis, and can be regulated by CLA or Rosi possibly via activating PPARγ.

Rosiglitazone regulates IL-6-stimulated lipolysis in porcine adipocytes

Interleukin (IL)-6, a proinflammatory cytokine, stimulates adipocyte lipolysis and induces insulin resistance in obese and diabetic subjects. However, the effects of the anti-diabetic drug rosiglitazone on IL-6-stimulated lipolysis and the underlying molecular mechanism are largely unknown. In this study, we demonstrated that rosiglitazone suppressed IL-6-stimulated lipolysis in differentiated porcine adipocytes by inactivation of extracellular signal-related kinase (ERK). Meanwhile, rosiglitazone enhanced the lipolysis response of adipocytes to isoprenaline. In addition, rosiglitazone significantly reversed IL-6-induced down-regulation of several genes such as perilipin A, peroxisome proliferators activated receptor gamma (PPAR&gamma;), and fatty acid synthetase, as well as the up-regulation of IL-6 mRNA. However, mRNA expression of PPAR&gamma; coactivator-1 alpha (PCG-1&alpha;) was enhanced by rosiglitazone in IL-6-stimulated adipocytes. These results indicate that rosiglitazone suppresses IL-6-stimulated lipolysis in porcine adipocytes through multiple molecular mechanisms.

Different effects of pioglitazone and rosiglitazone on lipid metabolism in mouse cultured liver explants

BACKGROUND

Pioglitazone (PIO) and rosiglitazone (ROSI) are widely used as oral antidiabetic agents for treatment of type 2 diabetes. Although these medications exert similar effects on blood glucose, recent clinical studies indicated that PIO has a more pronounced beneficial effect on lipid parameters than ROSI. In order to get further insight into the lipid effects of both drugs, we tested whether PIO, compared to ROSI, could exert direct effects on lipid liver metabolism in relation with plasma lipids.

METHODS

We performed in vitro studies using mice liver slices incubated 21 h either with ROSI (1 micromol/L) or PIO (7.5 micromol/L).

RESULTS

We showed that both glitazones slightly reduced HMG-CoA reductase mRNA levels at the same degree but only PIO reduced intracellular cholesterol content, suggesting an alteration of cholesterol uptake rather than an inhibition of cholesterol biosynthesis. This concept was supported by the reduction of scavenger receptor class B type I expression, hepatic lipase activity and high-density lipoprotein cholesterol uptake in PIO-treated liver explants. Conversely, hepatic lipase mRNA levels were increased 3.5-fold. ROSI, but not PIO, induced acetyl-CoA carboxylase and fatty acid synthase gene expression and increased apoB secretion suggesting a stimulation of lipogenesis. Concurrently, peroxisome proliferator-activated receptor-gamma mRNA levels were induced by ROSI and not significantly changed by PIO. Besides, PIO appeared to be a more potent activator of AMP-Activated Protein Kinase than ROSI.

CONCLUSIONS

PIO and ROSI exert specific direct effects on liver and extrapolating these data to humans could explain the significant improvements in plasma lipids observed in diabetic patients treated with PIO.

Mechanisms of adipose tissue redistribution with rosiglitazone treatment in various adipose depots

Treatment with thiazolidinediones (TZDs) improves glucose homeostasis by increasing insulin sensitivity, but it also leads to weight gain. Our hypothesis was that, in individual adipose depots, there is depot specificity for lipid storage and energy expenditure genes after TZD treatment. After 5 weeks of rosiglitazone treatment on Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an animal model of type 2 diabetes mellitus with obesity, and Long-Evans Tokushima Otsuka rats as controls, we measured changes in lipid storage and energy expenditure gene expression in various adipose depots, such as mesenteric and nonmesenteric adipose tissues (subcutaneous, epididymal, and retroperitoneal). Mesenteric fat masses did not change after TZD treatment in OLETF rats, but nonmesenteric fat masses increased. Messenger RNA expression of lipid storage genes increased in nonmesenteric fat, but energy expenditure gene expression increased in mesenteric fat after rosiglitazone treatment. In conclusion, our findings suggest that TZD treatment may be associated with the depot-specific effects of lipid storage and energy expenditure genes on fat redistribution in individual adipose tissues in OLETF rats.

PAT proteins, an ancient family of lipid droplet proteins that regulate cellular lipid stores

The PAT family of lipid droplet proteins includes 5 members in mammals: perilipin, adipose differentiation-related protein (ADRP), tail-interacting protein of 47 kDa (TIP47), S3-12, and OXPAT. Members of this family are also present in evolutionarily distant organisms, including insects, slime molds and fungi. All PAT proteins share sequence similarity and the ability to bind intracellular lipid droplets, either constitutively or in response to metabolic stimuli, such as increased lipid flux into or out of lipid droplets. Positioned at the lipid droplet surface, PAT proteins manage access of other proteins (lipases) to the lipid esters within the lipid droplet core and can interact with cellular machinery important for lipid droplet biogenesis. Genetic variations in the gene for the best-characterized of the mammalian PAT proteins, perilipin, have been associated with metabolic phenotypes, including type 2 diabetes mellitus and obesity. In this review, we discuss how the PAT proteins regulate cellular lipid metabolism both in mammals and in model organisms.

Cidea is associated with lipid droplets and insulin sensitivity in humans

Storage of energy as triglyceride in large adipose-specific lipid droplets is a fundamental need in all mammals. Efficient sequestration of fat in adipocytes also prevents fatty acid overload in skeletal muscle and liver, which can impair insulin signaling. Here we report that the Cide domain-containing protein Cidea, previously thought to be a mitochondrial protein, colocalizes around lipid droplets with perilipin, a regulator of lipolysis. Cidea-GFP greatly enhances lipid droplet size when ectopically expressed in preadipocytes or COS cells. These results explain previous findings showing that depletion of Cidea with RNAi markedly elevates lipolysis in human adipocytes. Like perilipin, Cidea and the related lipid droplet protein Cidec/FSP27 are controlled by peroxisome proliferator-activated receptor gamma (PPARgamma). Treatment of lean or obese mice with the PPARgamma agonist rosiglitazone markedly up-regulates Cidea expression in white adipose tissue (WAT), increasing lipid deposition. Strikingly, in both omental and s.c. WAT from BMI-matched obese humans, expression of Cidea, Cidec/FSP27, and perilipin correlates positively with insulin sensitivity (HOMA-IR index). Thus, Cidea and other lipid droplet proteins define a novel, highly regulated pathway of triglyceride deposition in human WAT. The data support a model whereby failure of this pathway results in ectopic lipid accumulation, insulin resistance, and its associated comorbidities in humans.

Adipocyte dysfunctions linking obesity to insulin resistance and type 2 diabetes

Acquired resistance to the action of insulin to stimulate glucose transport in skeletal muscle is associated with obesity and promotes the development of type 2 diabetes. In skeletal muscle, insulin resistance can result from high levels of circulating fatty acids that disrupt insulin signalling pathways. However, the severity of insulin resistance varies greatly among obese people. Here we postulate that this variability might reflect differences in levels of lipid-droplet proteins that promote the sequestration of fatty acids within adipocytes in the form of triglycerides, thereby lowering exposure of skeletal muscle to the inhibitory effects of fatty acids.