Lipocalin 2 is a selective modulator of peroxisome proliferator-activated receptor-gamma activation and function in lipid homeostasis and energy expenditure.
ABSTRACT: We have previously identified lipocalin 2 (Lcn2) as a cytokine playing a critical role in the regulation of body fat mass, lipid metabolism, and insulin resistance. Lcn2 deficiency reduces PPAR? gene expression in adipocytes. In this study, we investigated the role of Lcn2 in PPAR? activation and function via assessing the insulin sensitization and fatty acid (FA) homeostasis of PPAR? agonist in high-fat diet (HFD)-induced obesity in Lcn2(-/-) mice. We found that rosiglitazone (Rosi) significantly improved insulin sensitivity in Lcn2(-/-) mice as effectively as in wild-type (WT) mice; unfed-state levels of blood glucose, free FAs, and triglycerides (TGs) were significantly reduced after a 25-d treatment of Rosi in Lcn2(-/-) mice. However, Rosi action on fat deposition and FA homeostasis was altered; Rosi-induced body weight and subcutaneous fat gain and liver lipid accumulation were markedly lessened in Lcn2(-/-) mice. The results of in vivo metabolic labeling showed that Rosi markedly reduced de novo lipogenesis in adipose tissue of Lcn2(-/-) mice. In brown adipose tissue (BAT), the expression of the genes functioning in TG hydrolysis and mitochondrial oxidation was up-regulated more in Lcn2(-/-) than in WT mice. Most strikingly, Rosi stimulated significantly higher levels of uncoupling protein-1 expression in BAT, and completely rescued cold intolerance in Lcn2(-/-) mice. We demonstrate that Lcn2 is a critical selective modulator of PPAR? activation and function in lipid homeostasis and energy expenditure.
Project description:Lipocalin (LCN) 2 belongs to the lipocalin subfamily of low-molecular mass-secreted proteins that bind small hydrophobic molecules. LCN2 has been recently characterized as an adipose-derived cytokine, and its expression is upregulated in adipose tissue in genetically obese rodents. The objective of this study was to investigate the role of LCN2 in diet-induced insulin resistance and metabolic homeostasis in vivo.Systemic insulin sensitivity, adaptive thermogenesis, and serum metabolic and lipid profile were assessed in LCN2-deficient mice fed a high-fat diet (HFD) or regular chow diet.The molecular disruption of LCN2 in mice resulted in significantly potentiated diet-induced obesity, dyslipidemia, fatty liver disease, and insulin resistance. LCN2(-/-) mice exhibit impaired adaptive thermogenesis and cold intolerance. Gene expression patterns in white and brown adipose tissue, liver, and muscle indicate that LCN2(-/-) mice have increased hepatic gluconeogenesis, decreased mitochondrial oxidative capacity, impaired lipid metabolism, and increased inflammatory state under the HFD condition.LCN2 has a novel role in adaptive thermoregulation and diet-induced insulin resistance.
Project description:Emerging evidence indicates that epigenetic mechanisms like DNA methylation directly contribute to metabolic regulation. For example, we previously demonstrated that de novo DNA methyltransferase Dnmt3a plays a causal role in the development of adipocyte insulin resistance. Recent studies suggest that DNA demethylation plays an important role in the developmental process of adipocytes. However, little is known about whether DNA demethylase ten-eleven translocation (TET) proteins regulate the metabolic functions of adipocytes. METHODS:The expression of Tet genes was assessed in the fractionated adipocytes of chow- and high fat diet-fed C57/Bl6 mice using qPCR and western blotting. The effect of Tet2 gain- or loss-of-function in fully mature 3T3-L1 adipocytes in the presence/absence of Rosiglitazone (Rosi) and TNF-? on insulin sensitivity was using the insulin-stimulated glucose uptake and insulin signaling assays. Gene expression and DNA methylation analyses of PPAR? target genes was performed in the same setting. In addition, PPAR? reporter assays, co-immunoprecipitation assays, PPAR? ChIP-PCR analyses were performed. RESULTS:We found that adipose expression of TET2, alone among its family members, was significantly reduced in diet-induced insulin resistance. TET2 gain-of-function was sufficient to promote insulin sensitivity while loss-of-function was necessary to facilitate insulin sensitization in response to the PPAR? agonist Rosiglitazone (Rosi) in cultured adipocytes. Consistent with this, TET2 was required for Rosi-dependent gene activation of certain PPAR? targets accompanied by changes in DNA demethylation at the promoter regions. Furthermore, TET2 was necessary to sustain PPAR? binding to target loci upon activation with Rosi via physical interaction with PPAR?. CONCLUSIONS:Our data demonstrate that TET2 works as an epigenetic regulator of Rosi-mediated insulin sensitization and transcriptional regulation in adipocytes.
Project description:Neutrophil gelatinase-associated lipocalin (NGAL, lipocalin 2 or LCN2) is an iron carrier protein whose circulating level is increased by kidney injury, bacterial infection and obesity, but its metabolic consequence remains elusive. To study physiological role of LCN2 in energy homeostasis, we challenged female Lcn2 knockout (KO) and wild-type (WT) mice with high fat diet (HFD) or cold exposure. Under normal diet, physical constitutions of Lcn2 KO and WT mice were indistinguishable. During HFD treatment, Lcn2 KO mice exhibited larger brown adipose tissues (BAT), consumed more oxygen, ate more food and gained less body weights as compared to WT mice. When exposed to 4?°C, KO mice showed higher body temperature and more intense <sup>18</sup>F-fluorodeoxyglucose uptake in BAT, which were cancelled by ?3 adrenergic receptor blocker or iron-loaded (but not iron-free) LCN2 administration. These findings suggest that circulating LCN2 possesses obesity-promoting and anti-thermogenic effects through inhibition of BAT activity in an iron-dependent manner.
Project description:Treatment with PPAR? agonists in vivo improves human adipocyte metabolism, but the cellular mechanisms and possible depot differences in responsiveness to their effects are poorly understood. To examine the ex vivo metabolic effects of rosiglitazone (Rosi), we cultured explants of human visceral (omental) and abdominal subcutaneous adipose tissues for 7 days. Rosi increased mRNA levels of transcriptional regulators of brite/beige adipocytes (PGC1?, PRDM16), triglyceride synthesis (GPAT3, DGAT1), and lipolysis (ATGL) similarly in adipose tissues from both depots. In parallel, Rosi increased key modulators of FA oxidation (UCP1, FABP3, PLIN5 protein), rates of FA oxidation, and protein levels of electron transport complexes, suggesting an enhanced respiratory capacity as confirmed in newly differentiated adipocytes. Rosi led to the formation of small lipid droplets (SLDs) around the adipocyte central lipid droplet; each SLD was decorated with redistributed mitochondria that colocalized with PLIN5. SLD maintenance required lipolysis and FA reesterification. Rosi thus coordinated a structural and metabolic remodeling in adipocytes from both visceral and subcutaneous depots that enhanced oxidative capacity. Selective targeting of these cellular mechanisms to improve adipocyte FA handling may provide a new approach to treat metabolic complications of obesity and diabetes.
Project description:Purpose: To study the role of PPAR nuclear receptors in brown fat. Methods: mRNA-sequencing was performed on brown adipose tissue from mice on diets with or without added rosiglitazone or fenofibrate. Sequence reads that passed quality filters were analyzed at the transcript isoform level with RNA-Seq Unified Mapper. Results: We identified genes that were induced or repressed by either PPAR agonist, and approximately three-fold more genes were significantly regulated by rosiglitazone (rosi, a PPARg agonist) than by fenofibrate (feno, a PPARa agonist). Those genes induced by either drug were enriched for expected lipid metabolic pathways, while down-regulated genes fell in pathways of uncertain relevance. Most genes were selectively regulated by one of the two PPAR agonists, with few regulated by both. Only 34 genes were induced by both PPAR agonists (~10% of rosi-induced genes and ~25% of feno-induced genes), and these were enriched for mitochondrial functionrelated pathways, including fatty acid β-oxidation. Conclusions: These data suggest that PPARγ agonists have stronger effects on BAT than PPARα agonists, yet those genes activated by both PPAR agonists may be particularly relevant to BAT function. Overall design: Brown adipose tissue mRNA profiles of control and PPAR agonist-treated mice were generated by deep sequencing
Project description:Peroxisome proliferator activated receptor gamma (PPAR?) controls both glucose metabolism and an allocation of marrow mesenchymal stem cells (MSCs) toward osteoblast and adipocyte lineages. Its activity is determined by interaction with a ligand which directs posttranscriptional modifications of PPAR? protein including dephosphorylation of Ser112 and Ser273, which results in acquiring of pro-adipocytic and insulin-sensitizing activities, respectively. PPAR? full agonist TZD rosiglitazone (ROSI) decreases phosphorylation of both Ser112 and Ser273 and its prolonged use causes bone loss in part due to diversion of MSCs differentiation from osteoblastic toward adipocytic lineage. Telmisartan (TEL), an anti-hypertensive drug from the class of angiotensin receptor blockers, also acts as a partial PPAR? agonist with insulin-sensitizing and a weak pro-adipocytic activity. TEL decreased S273pPPAR? and did not affect S112pPPAR? levels in a model of marrow MSC differentiation, U-33/?2 cells. In contrast to ROSI, TEL did not affect osteoblast phenotype and actively blocked ROSI-induced anti-osteoblastic activity and dephosphorylation of S112pPPAR?. The effect of TEL on bone was tested side-by-side with ROSI. In contrast to ROSI, TEL administration did not affect bone mass and bone biomechanical properties measured by micro-indentation method and did not induce fat accumulation in bone, and it partially protected from ROSI-induced bone loss. In addition, TEL induced "browning" of epididymal white adipose tissue marked by increased expression of UCP1, FoxC2, Wnt10b and IGFBP2 and increased overall energy expenditure. These studies point to the complexity of mechanisms by which PPAR? acquires anti-osteoblastic and pro-adipocytic activities and suggest an importance of Ser112 phosphorylation status as being a part of the mechanism regulating this process. These studies showed that TEL acts as a full PPAR? agonist for insulin-sensitizing activity and as a partial agonist/partial antagonist for pro-adipocytic and anti-osteoblastic activities. They also suggest a relationship between PPAR? fat "browning" activity and a lack of anti-osteoblastic activity.
Project description:The purpose of this experiment was to determine the antidiabetic and lipid-lowering effects of (-)-epicatechin-3-O-?-D-allopyranoside (BB) from the roots and stems of Davallia formosana in mice. Animal treatment was induced by high-fat diet (HFD) or low-fat diet (control diet, CD). After eight weeks of HFD or CD exposure, the HFD mice were treating with BB or rosiglitazone (Rosi) or fenofibrate (Feno) or water through gavage for another four weeks. However, at 12 weeks, the HFD-fed group had enhanced blood levels of glucose, triglyceride (TG), and insulin. BB treatment significantly decreased blood glucose, TG, and insulin levels. Moreover, visceral fat weights were enhanced in HFD-fed mice, accompanied by increased blood leptin concentrations and decreased adiponectin levels, which were reversed by treatment with BB. Muscular membrane protein levels of glucose transporter 4 (GLUT4) were reduced in HFD-fed mice and significantly enhanced upon administration of BB, Rosi, and Feno. Moreover, BB treatment markedly increased hepatic and skeletal muscular expression levels of phosphorylation of AMP-activated (adenosine monophosphate) protein kinase (phospho-AMPK). BB also decreased hepatic mRNA levels of phosphenolpyruvate carboxykinase (PEPCK), which are associated with a decrease in hepatic glucose production. BB-exerted hypotriglyceridemic activity may be partly associated with increased mRNA levels of peroxisome proliferator activated receptor ? (PPAR?), and with reduced hepatic glycerol-3-phosphate acyltransferase (GPAT) mRNA levels in the liver, which decreased triacylglycerol synthesis. Nevertheless, we demonstrated BB was a useful approach for the management of type 2 diabetes and dyslipidemia in this animal model.
Project description:Peroxisome proliferator-activated receptor-? (PPAR?) is a dietary lipid sensor, whose activation results in hypolipidemic effects. In this study, we investigated whether PPAR? activation affects energy metabolism in white adipose tissue (WAT). Activation of PPAR? 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 PPAR? 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 PPAR? activation. PPAR? 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 PPAR?-deficient mice. Bezafibrate treatment enhanced FA oxidation in isolated adipocytes, suppressing adipocyte hypertrophy. Chromatin immunoprecipitation (ChIP) assay revealed that PPAR? 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 PPAR? affects energy metabolism in adipocytes, and PPAR? activation in WAT may contribute to the clinical effects of fibrate drugs.
Project description: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.
Project description:BACKGROUND:Beige adipocytes comprise a unique thermogenic cell type in the white adipose tissue (WAT) of rodents and humans, and play a critical role in energy homeostasis. In this scenario, recruitment of beige cells has been an important focus of interest for the development of novel therapeutic strategies to treat obesity. PPAR? activation by full agonists (thiazolidinediones, TZDs) drives the appearance of beige cells, a process so-called browning of WAT. However, this does not translate into increased energy expenditure, and TZDs are associated with weight gain. Partial PPAR? agonists, on the other hand, do not induce weight gain, but have not been shown to drive WAT browning. The present study was designed to investigate the effects of GQ-16 on BAT and on browning of WAT in obese mice. METHODS:Male Swiss mice with obesity and hyperglycemia induced by high fat diet were treated with vehicle, rosiglitazone (4 mg/kg/d) or the TZD-derived partial PPAR? agonist GQ-16 (40 mg/kg/d) for 14 days. Fasting blood glucose, aspartate aminotransferase, alanine aminotransferase and lipid profile were measured. WAT and brown adipose tissue (BAT) depots were excised for determination of adiposity, relative expression of Ucp-1, Cidea, Prdm16, Cd40 and Tmem26 by RT-qPCR, histological analysis, and UCP-1 protein expression analysis by immunohistochemistry. Liver samples were also removed for histological analysis and determination of hepatic triglyceride content. RESULTS:GQ-16 treatment reduced high fat diet-induced weight gain in mice despite increasing energy intake. This was accompanied by reduced epididymal fat mass, reduced liver triglyceride content, morphological signs of increased BAT activity, increased expression of thermogenesis-related genes in interscapular BAT and epididymal WAT, and increased UCP-1 protein expression in interscapular BAT and in epididymal and inguinal WAT. CONCLUSION:This study suggests for the first time that a partial PPAR? agonist may increase BAT activity and induce the expression of thermogenesis-related genes in visceral WAT. GENERAL SIGNIFICANCE:These findings suggest that PPAR? activity might be modulated by partial agonists to induce WAT browning and treat obesity.