Activation of peroxisome proliferator-activated receptor-alpha stimulates both differentiation and fatty acid oxidation in adipocytes

Peroxisome proliferator-activated receptor-α (PPARα) is a dietary lipid sensor, whose activation results in hypolipidemic effects. In this study, we investigated whether PPARα activation affects energy metabolism in white adipose tissue (WAT). Activation of PPARα by its agonist (bezafibrate) markedly reduced adiposity in KK mice fed a high-fat diet. In 3T3-L1 adipocytes, addition of GW7647, a highly specific PPARα agonist, during adipocyte differentiation enhanced glycerol-3-phosphate dehydrogenase activity, insulin-stimulated glucose uptake, and adipogenic gene expression. However, triglyceride accumulation was not increased by PPARα activation. PPARα activation induced expression of target genes involved in FA oxidation and stimulated FA oxidation. In WAT of KK mice treated with bezafibrate, both adipogenic and FA oxidation-related genes were significantly upregulated. These changes in mRNA expression were not observed in PPARα-deficient mice. Bezafibrate treatment enhanced FA oxidation in isolated adipocytes, suppressing adipocyte hypertrophy. Chromatin immunoprecipitation (ChIP) assay revealed that PPARα was recruited to promoter regions of both adipogenic and FA oxidation-related genes in the presence of GW7647 in 3T3-L1 adipocytes. These findings indicate that the activation of PPARα affects energy metabolism in adipocytes, and PPARα activation in WAT may contribute to the clinical effects of fibrate drugs.     

Impact of Doxorubicin Treatment on the Physiological Functions of White Adipose Tissue

White adipose tissue (WAT) plays a fundamental role in maintaining energy balance and important endocrine functions. The loss of WAT modifies adipokine secretion and disrupts homeostasis, potentially leading to severe metabolic effects and a reduced quality of life. Doxorubicin is a chemotherapeutic agent used clinically because of its good effectiveness against various types of cancer. However, doxorubicin has deleterious effects in many healthy tissues, including WAT, liver, and skeletal and cardiac muscles. Our objective was to investigate the effects of doxorubicin on white adipocytes through in vivo and in vitro experiments. Doxorubicin reduced the uptake of glucose by retroperitoneal adipocytes and 3T3-L1 cells via the inhibition of AMP-activated protein kinase Thr172 phosphorylation and glucose transporter 4 content. Doxorubicin also reduced the serum level of adiponectin and, to a greater extent, the expression of genes encoding lipogenic (Fas and Acc) and adipogenic factors (Pparg, C/ebpa, and Srebp1c) in retroperitoneal adipose tissue. In addition, doxorubicin inhibited both lipogenesis and lipolysis and reduced the hormone-sensitive lipase and adipose tissue triacylglycerol lipase protein levels. Therefore, our results demonstrate the impact of doxorubicin on WAT. These results are important to understand some side effects observed in patients receiving chemotherapy and should encourage new adjuvant treatments that aim to inhibit these side effects.     

Prohibitin deficiency causes opposing lipid metabolism between 3T3-L1 adipocytes and Clone 9 hepatocytes

Prohibitin (PHB) is a highly conserved protein in eukaryotic cells that are present in multiple cellular compartments and has potential roles as a tumor suppressor, an anti-proliferative protein, a regulator of cell-cycle progression and in apoptosis. In the present study, we generated PHB-deficient 3T3-L1 adipocytes and Clone 9 (C9) hepatocytes by oligonucleotide siRNA and investigated whether PHB affect lipid metabolism. It was revealed that PHB deficiency caused opposing lipid metabolism between the two cell models. PHB deficiency increased expression of adipogenic, lipogenic, and other lipid metabolic proteins in 3T3-L1 adipocytes, whereas significantly decreased the levels of those proteins in C9 cells. Collectively, PHB deficiency promoted lipid metabolism in 3T3-L1 adipocytes while it aggravated lipid metabolism in C9 hepatocytes.     

Fargesin improves lipid and glucose metabolism in 3T3-L1 adipocytes and high-fat diet-induced obese mice

This study examined the effects of fargesin, a neolignan isolated from Magnolia plants, on obesity and insulin resistance and the possible mechanisms involved in these effects in 3T3-L1 adipocytes and high-fat diet (HFD)-induced obese mice. Fargesin promoted the glucose uptake in 3T3-L1 adipocytes. In HFD-induced obese mice, fargesin decreased the body weight gain, white adipose tissue (WAT), and plasma triglyceride, non-esterified fatty acid and glucose levels, and improved the glucose tolerance. Fargesin increased glucose transporter 4 (GLUT4) protein expression and phosphorylation of Akt, AMP-activated protein kinase (AMPK), and acetyl-CoA carboxylase (ACC) in both 3T3-L1 adipocytes and WAT of HFD-induced obese mice. Fargesin also decreased the mRNA expression levels of fatty acid oxidation-related genes, such as peroxisome proliferator-activated receptor α (PPARα), carnitine palmitoyltransferase-1 (CPT-1), uncoupling protein-2 (UCP-2) and leptin in WAT. Taken together, the present findings suggest that fargesin improves dyslipidemia and hyperglycemia by activating Akt and AMPK in WAT. ? 2012 International Union of Biochemistry and Molecular Biology, Inc.     

Raspberry ketone induces brown-like adipocyte formation through suppression of autophagy in adipocytes and adipose tissue

Promoting white adipose tissue (WAT) to acquire brown-like characteristics is a promising approach for obesity treatment. Although raspberry ketone (RK) has been reported to possess antiobesity activity, its effects on the formation of brown-like adipocytes remain unclear. Therefore, we investigated the effects and underlying mechanism of RK on WAT browning in 3T3-L1 adipocytes and rats with ovariectomy (Ovx)-induced obesity. RK (100 μM) significantly induced browning of 3T3-L1 cells by increasing mitochondrial biogenesis and the expression of browning-specific proteins (PR domain containing 16, PRDM16; peroxisome proliferator-activated receptor gamma coactivator 1-alpha, PGC-1α; uncoupling protein-1, UCP-1) and lipolytic enzymes (hormone-sensitive lipase and adipose triglyceride lipase). RK significantly reduced the expression of the autophagy-related protein Atg12 and increased the expression of p62 and heme oxygenase 1 (HO-1). Additionally, these effects of RK were reversed by the HO-1 inhibitor SnPP (20 μM). In addition, RK (160 mg/kg, gavage, for 8 weeks) significantly reduced body weight gain (Ovx+RK, 191.8 ± 4.6 g vs. Ovx, 223.6 ± 5.9; P < .05), food intake, the amount of inguinal adipose tissue (Ovx+RK, 9.05 ± 1.1 g vs Ovx, 12.9 ± 0.92 g; P < .05) and the size of white adipocytes in Ovx rats. Moreover, compared to expression in the Ovx group, the levels of browning-specific proteins were significantly higher and the levels of autophagy-related proteins were significantly lower in the Ovx+RK group. Therefore, this study elucidated the mechanism associated with RK-induced WAT browning and thus provides evidence to support the clinical use of RK for obesity treatment.     

Caudatin suppresses adipogenesis in 3T3-L1 adipocytes and reduces body weight gain in high-fat diet-fed mice through activation of hedgehog signaling

BackgroundThe regulative effects of caudatin, a C-21 steroid that is identified from Cynanchum bungee roots, on adipogenesis and obesity have not been studied. Many studies have demonstrated that the activation of hedgehog (Hh) signaling can help prevent obesity. Therefore, we hypothesized that caudatin can inhibit adipogenesis and obesity via activating the Hh signaling pathway.MethodsTo investigate the effects of caudatin on adipogenesis in 3T3-L1 preadipocytes and high-fat diet induced obesity in C57BL/6 mice, in vitro and in vivo experiments were performed. For in vitro evaluation, Oil red O staining were used to represent lipid accumulation in differentiated 3T3-L1 adipocytes. For in vivo assessment, male 5 week-old C57BL/6 mice were fed with standard chow diet, high-fat diet (HFD), HFD with 25 mg/kg caudatin, HFD with 1mg/kg purmorpharmine for 10 weeks, respectively. Hh signaling and key adipogenic marker involved in adipogenesis were evaluated by real-time PCR and western blot. The adipocyte size of white adopose tissue and lipid storage of liver were visualized by hematoxylin and eosin staining. In addition, the expression of Gli1 and peroxisome proliferator-activated receptor γ (PPARγ) in white adipose tissue were investigated by immunohistochemistry staining.ResultsCaudatin suppressed the accumulation of lipid droplets and downregulated the expression of key adipogenic factors, i.e., peroxisome proliferator-activated receptor γ PPARγ and CCAAT-enhancer binding protein α (C/EBPα), through activating Hh signaling in differentiated 3T3-L1 cells. Furthermore, caudatin and the Hh activator purmorpharmine significantly decreased body weight gain and white adipose tissue (WAT) weight in HFD-induced mice and affected adipogenic markers and Hh signaling mediators in WAT, which were in line with the in vitro experimental results.ConclusionTo our best knowledge, it is the first report to demonstrate that caudatin downregulated adipocyte differentiation and suppressed HFD-induced body weight gain through activating the Hh signaling pathway, suggesting that caudatin can potentially counteract obesity.     

Bromocriptine inhibits adipogenesis and lipogenesis by agonistic action on α2-adrenergic receptor in 3T3-L1 adipocyte cells

The primary goals of the present study were to investigate the inhibitory effects of bromocriptine (BC) on adipogenesis and lipogenesis in 3T3-L1 adipocyte cells as well as to elucidate its molecular mechanism of action. Adipogenic and lipogenic capacity of BC-treated cells was evaluated by oil red-O staining, triglyceride content assay, real-time RT-PCR and immunoblotting. To determine the mechanism responsible for the anti-obesity effect of BC, we applied two methods. Firstly, we knocked down dopamine D2 receptor (D2R) up to 50 % using siRNA. Secondly, we blocked the activity of α2-adrenergic receptor (α2-AR) by yohimbine treatment and monitored its effects on adipogenic and lipogenic events in 3T3-L1 cells. BC decreased the expression levels of adipogenic activators, including Pparα, Pparγ, and Cebpα, as well as major lipogenic target genes, including Me1, Acc1, 6Pgd, Fasn, and Prkaa1. Moreover, BC markedly reduced intracellular nitric oxide formation in a dose-dependent manner and expression of pro-inflammatory genes, Tnfα and Il6, which reflects attenuated pro-inflammatory responses. Further, upon treatment with BC, D2R-deficient cells displayed a significant decrease in lipogenic activity compared to control cells, whereas yohimbine-treated cells exhibited no reduction in lipogenic activity. BC can effectively attenuate adipogenesis and lipogenesis in 3T3-L1 cells by downregulating the expression of lipogenic genes and proteins. Our current experimental data collectively establish that the anti-obesity effects of BC are not D2R-dependent but result from the action of α2-AR in 3T3-L1 adipocytes.     

Thyroid hormone stimulates adipocyte differentiation of 3T3 cells

Triiodothyronine added at 0.1 nM to 3T3-F442A cells cultured in adipogenic medium having endogenous hormone concentrations similar to those of hypothyroid serum stimulated adipose conversion; activities of both lipogenic enzymes, glycerophosphate dehydrogenase and malic enzyme, increased with hormone treatment. The number of adipocytes was also augmented by L-T3 addition but the number of fat cell clusters remained the same as compared to non-treated cultures, suggesting that thyroid hormone increased the number of adipocytes probably through stimulating selective multiplication of precursor adipose cells. Hormone addition to cells cultured with non-adipogenic medium did not promote conversion showing that L-T3 is not an adipogenic factor by itself. Triiodothyronine added at concentrations similar to those found in hyperthyroidism, from 10 nM up to 10 µM, also increased the proportion of adipocytes without changing the number of fat cell clusters, but they decreased the activity of both lipogenic enzymes and lipid accumulation in mature adipocytes. It can be concluded that during 3T3-F442A differentiation into adipocytes L-T3 increases the number of differentiated adipocytes and, at low concentrations, also enhances lipogenic enzyme activities, whereas at the hyperthyroid hormone levels these enzyme activities are significantly reduced, remaining at levels similar to those of cells cultured with hypothyroid medium. This cloned cell line seems to be a useful model to study thyroid hormone action at both molecular and cellular level.     

Long chain acyl CoA synthetase 1 and gelsolin are oppositely regulated in adipogenesis and lipogenesis

Our previous proteomics study revealed that long chain acyl CoA synthetase 1 (ACSL1) and gelsolin (GSN) are oppositely regulated in white adipose tissue of diet-induced obese rats. To firmly establish these proteins as mediators of adipogenic and/or lipogenic events, we efficiently knocked down the Acsl1 and Gsn genes using siRNA in 3T3-L1 adipocyte cells. Expectedly, Acsl1 knockdown stimulated expression of lipogenic genes. Interestingly, Gsn knockdown suppressed expression of lipogenic genes but strikingly increased that of Tnfα and Il6, which may have connections with lipolytic capacity of these genes. Conclusively, we provide clear evidence that ACSL1 and GSN are potential target proteins in the context of obesity.     

Proteome analysis in adipose tissue of <Emphasis Type="Italic">ob/ob</Emphasis> mice in response to chitosan oligosaccharides treatment

Adipose tissue plays a central role in the development of obesity, and thus characterization of the molecular changes related to obesity in this tissue is a main concern. Recently we identified chitosan oligosaccharides (CO) as a potent adipogenic inhibitor in 3T3-L1 cells. In the current study, a proteomic approach was used to investigate the anti-obesity effect of CO in white adipose tissue of ob/ob mice. CO administration significantly lowered body weight gain and epididymal WAT mass compared to control animals. In addition, twenty-five proteins were found to be differentially expressed between the two groups of animals in response to CO treatment. Expression changes in Karyopherin beta 1, indoleamine-pyrrole 2,3-dioxygenase, and retinoic acid binding protein were associated here for the first time with obesity. Immunoblotting studies of adipocyte protein 2 (aP2) and aquaporin-7 also showed amelioration in their levels in WAT. Furthermore, the results of adipose tissue specific gene expressions of aP2, adiponectin, TNF-α, and IL-6 were in good agreement with improved levels of obesity. Gene expression of PPARg and SREBP-1c were also down-regulated by CO treatment. The results suggest that the anti-obesity effect of CO might be mediated by the modulation of adipokines and adipose tissue specific genes.     

NGF gene expression and secretion in white adipose tissue: regulation in 3T3-L1 adipocytes by hormones and inflammatory cytokines

The sympathetic nervous system plays a central role in lipolysis and the production of leptin in white adipose tissue (WAT). In this study, we have examined whether nerve growth factor (NGF), a target-derived neurotropin that is a key signal in the development and survival of sympathetic neurons, is expressed and secreted by white adipocytes. NGF mRNA was detected by RT-PCR in the major WAT depots of mice (epididymal, perirenal, omental, mesenteric, subcutaneous) and in human fat (subcutaneous, omental). In mouse WAT, NGF expression was observed in mature adipocytes and in stromal vascular cells. NGF expression was also evident in 3T3-L1 cells before and after differentiation into adipocytes. NGF protein, measured by ELISA, was secreted from 3T3-L1 cells, release being higher before differentiation. Addition of the sympathetic agonists norepinephrine, isoprenaline, or BRL-37344 (beta(3)-agonist) led to falls in NGF gene expression and secretion by 3T3-L1 adipocytes, as did IL-6 and the PPARgamma agonist rosiglitazone. A substantial decrease in NGF expression and secretion occurred with dexamethasone. In contrast, LPS increased NGF mRNA levels and NGF secretion. A major increase in NGF mRNA level (9-fold) and NGF secretion (相似文献   

Critical role of the peroxisomal protein PEX16 in white adipocyte development and lipid homeostasis

The importance of peroxisomes for adipocyte function is poorly understood. Herein, we provide insights into the critical role of peroxin 16 (PEX16)-mediated peroxisome biogenesis in adipocyte development and lipid metabolism. Pex16 is highly expressed in adipose tissues and upregulated during adipogenesis of murine and human cells. We demonstrate that Pex16 is a target gene of the adipogenesis “master-regulator” PPARγ. Stable silencing of Pex16 in 3T3-L1 cells strongly reduced the number of peroxisomes while mitochondrial number was unaffected. Concomitantly, peroxisomal fatty acid (FA) oxidation was reduced, thereby causing accumulation of long- and very long-chain (polyunsaturated) FAs and reduction of odd-chain FAs. Further, Pex16-silencing decreased cellular oxygen consumption and increased FA release. Additionally, silencing of Pex16 impaired adipocyte differentiation, lipogenic and adipogenic marker gene expression, and cellular triglyceride stores. Addition of PPARγ agonist rosiglitazone and peroxisome-related lipid species to Pex16-silenced 3T3-L1 cells rescued adipogenesis. These data provide evidence that PEX16 is required for peroxisome biogenesis and highlights the relevance of peroxisomes for adipogenesis and adipocyte lipid metabolism.