Farnesyl pyrophosphate regulates adipocyte functions as an endogenous PPARγ agonist

Metabolite-derived damage-associated molecular patterns in immunological diseases

Damage-associated molecular patterns (DAMPs) are typically derived from the endogenous elements of necrosis cells and can trigger inflammatory responses by activating DAMPs-sensing receptors on immune cells. Failure to clear DAMPs may lead to persistent inflammation, thereby contributing to the pathogenesis of immunological diseases. This review focuses on a newly recognized class of DAMPs derived from lipid, glucose, nucleotide, and amino acid metabolic pathways, which are then termed as metabolite-derived DAMPs. This review summarizes the reported molecular mechanisms of these metabolite-derived DAMPs in exacerbating inflammation responses, which may attribute to the pathology of certain types of immunological diseases. Additionally, this review also highlights both direct and indirect clinical interventions that have been explored to mitigate the pathological effects of these DAMPs. By summarizing our current understanding of metabolite-derived DAMPs, this review aims to inspire future thoughts and endeavors on targeted medicinal interventions and the development of therapies for immunological diseases.

Cardiac maturation

The heart undergoes a dynamic maturation process following birth, in response to a wide range of stimuli, including both physiological and pathological cues. This process entails substantial re-programming of mitochondrial energy metabolism coincident with the emergence of specialized structural and contractile machinery to meet the demands of the adult heart. Many components of this program revert to a more "fetal" format during development of pathological cardiac hypertrophy and heart failure. In this review, emphasis is placed on recent progress in our understanding of the transcriptional control of cardiac maturation, encompassing the results of studies spanning from in vivo models to cardiomyocytes derived from human stem cells. The potential applications of this current state of knowledge to new translational avenues aimed at the treatment of heart failure is also addressed.

The role of peroxisome proliferator-activated receptor γ in lipid metabolism and inflammation in atherosclerosis

Cardiovascular disease events are the result of functional and structural abnormalities in the arteries and heart. Atherosclerosis is the main cause and pathological basis of cardiovascular diseases. Atherosclerosis is a multifactorial disease associated with dyslipidemia, inflammation, and oxidative stress, among which dyslipidemia and chronic inflammation occur in all processes. Under the influence of lipoproteins, the arterial intima causes inflammation, necrosis, fibrosis, and calcification, leading to plaque formation in specific parts of the artery, which further develops into plaque rupture and secondary thrombosis. Foam cell formation from macrophages is an early event in the development of atherosclerosis. Lipid uptake causes a vascular inflammatory response, and persistent inflammatory infiltration in the lesion area further promotes the development of the disease. Inhibition of macrophage differentiation into foam cell and reduction of the level of proinflammatory factors in macrophages can effectively alleviate the occurrence and development of atherosclerosis. Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand-activated nuclear receptor that plays an important antiatherosclerotic role by regulating triglyceride metabolism, lipid uptake, cholesterol efflux, macrophage polarity, and inhibiting inflammatory signaling pathways. In addition, PPARγ shifts its binding to ligands and co-activators or co-repressors of transcription of target genes through posttranslational modification, thereby affecting the regulation of its downstream target genes. Many ligand agonists have also been developed targeting PPARγ. In this review, we summarized the role of PPARγ in lipid metabolism and inflammation in development of atherosclerosis, the posttranslational regulatory mechanism of PPARγ, and further discusses the value of PPARγ as an antiatherosclerosis target.

Statins reduce castration-induced bone marrow adiposity and prostate cancer progression in bone

A fraction of patients undergoing androgen deprivation therapy (ADT) for advanced prostate cancer (PCa) will develop recurrent castrate-resistant PCa (CRPC) in bone. Strategies to prevent CRPC relapse in bone are lacking. Here we show that the cholesterol-lowering drugs statins decrease castration-induced bone marrow adiposity in the tumor microenvironment and reduce PCa progression in bone. Using primary bone marrow stromal cells (BMSC) and M2-10B4 cells, we showed that ADT increases bone marrow adiposity by enhancing BMSC-to-adipocyte transition in vitro. Knockdown of androgen receptor abrogated BMSC-to-adipocyte transition, suggesting an androgen receptor-dependent event. RNAseq analysis showed that androgens reduce the secretion of adipocyte hormones/cytokines including leptin during BMSC-to-adipocyte transition. Treatment of PCa C4-2b, C4-2B4, and PC3 cells with leptin led to an increase in cell cycle progression and nuclear Stat3. RNAseq analysis also showed that androgens inhibit cholesterol biosynthesis pathway, raising the possibility that inhibiting cholesterol biosynthesis may decrease BMSC-to-adipocyte transition. Indeed, statins decreased BMSC-to-adipocyte transition in vitro and castration-induced bone marrow adiposity in vivo. Statin pre-treatment reduced 22RV1 PCa progression in bone after ADT. Our findings with statin may provide one of the mechanisms to the clinical correlations that statin use in patients undergoing ADT seems to delay progression to "lethal" PCa.

Integrated Proteomics and Metabolomics Analysis of Perirenal Adipose Tissue in Obese Rabbits Treated with a Restricted Diet

In recent years, many people have shown an excess of fat accumulation. Known as obesity, this lesion poses an increased risk for multiple diseases, such as endocrine disease, diabetes, and cancer, and has reached epidemic proportions. Accompanied by the development of obesity, concern over body image and weight loss behavior is a growing social problem and public health threat, causing concern for many health professionals. However, the consequences of rapid weight loss remain largely unclear. Here, we applied an integrated proteomics and metabolomics analysis to investigate the effects of dieting on the proteins and metabolites in obese rabbits. Our study revealed that 343 differentially expressed proteins (136 upregulated and 207 downregulated) and 150 differentially expressed metabolites (91 upregulated and 59 downregulated) were identified. These molecules are mainly involved in the biological processes, including amino acid metabolism, lipid metabolism, and membrane and cytoskeleton reconstruction. The integrated analysis found that mevalonic acid, arachidonic acid, 15(S)-HpETE, cholecalciferol, hydrocortisone, lipoxin B4, lithocholic acid, etc. were associated with multiple pathways, and they may be the key factors to fight inflammation induced by a high-fat diet (HFD). Overall, this study provides further insight into the consequences of dieting-mediated weight loss and may contribute to the prevention and treatment of obesity.

Dysregulation of the mevalonate pathway during SARS-CoV-2 infection: An in silico study

SARS-CoV-2 triggers a dysregulated innate immune system activation. As the mevalonate pathway (MVP) prevents the activation of inflammasomes and cytokine release and regulates endosomal transport, compromised signaling could be associated with the pathobiology of COVID-19. Prior transcriptomic studies of host cells in response to SARS-CoV-2 infection have not reported to date the effects of SARS-CoV-2 on the MVP. In this study, we accessed public data sets to report in silico investigations into gene expression. In addition, we proposed candidate genes that are thought to have a direct association with the pathogenesis of COVID-19, and which may be dependent on signals derived from the MVP. Our results revealed dysregulation of genes involved in the MVP. These results were not found when investigating the gene expression data from host cells infected with H3N2 influenza virus, H1N1 influenza virus, or respiratory syncytial virus. Our manually curated gene set showed significant gene expression variability in A549 cells infected with SARS-CoV-2, as per Blanco-Melo et al. data set (GSE147507). In light of the present findings, SARS-CoV-2 could hijack the MVP, leading to hyperinflammatory responses. Prompt reconstitution of this pathway with available agents should be considered in future studies.

Long non-coding RNA 2310069B03Rik functions as a suppressor of Ucp1 expression under prolonged cold exposure in murine beige adipocytes

Specific conditions, such as exposure to cold, can induce the production of brown-like adipocytes in white adipose tissue. These adipocytes express high levels of uncoupling protein 1 (UCP1) and energy expended by generating heat. Thus, these are a potential target for the prevention or treatment of obesity. The present study involved a comprehensive analysis of the adipose tissue to understand the relationship between long non-coding RNA (lncRNA) 2310069B03Rik and UCP1. Cold exposure increased both lncRNA 2310069B03Rik and Ucp1 expression in inguinal white adipose tissue (iWAT). However, overexpression of lncRNA 2310069B03Rik suppressed the Ucp1 mRNA expression and the promoter activity of UCP1 in the iWAT primary adipocytes. In addition, compared to the early induction of Ucp1 expression by cold stimulation, the induction of lncRNA 2310069B03Rik expression was later. These results suggest that lncRNA 2310069B03Rik functions as a suppression factor of Ucp1 expression.

A new mouse model for noninvasive fluorescence-based monitoring of mitochondrial UCP1 expression

Mitochondrial uncoupling protein 1 (UCP1) is well known for its thermogenic function in brown adipose tissue (BAT). Since UCP1 expends energy on thermogenesis, UCP1 activation has been considered an approach to ameliorate obesity. As a tool for uncovering yet unknown mechanisms of UCP1 activation, we generated a transgenic mouse model in which UCP1 expression levels are reflected in fluorescence derived from monomeric red fluorescent protein 1 (mRFP1). In these UCP1-mRFP1 BAC transgenic mice, fluorescence intensity mimics the change in UCP1 expression levels evoked through physiological or pharmacological stimulation. This transgenic mouse model will be useful in the search for bioactive compounds with the ability to induce UCP1 and for revealing undiscovered mechanisms of BAT activation.

A review of the studies on food-derived factors which regulate energy metabolism via the modulation of lipid-sensing nuclear receptors

Obesity is one of the most important risk factors for chronic metabolic disorders. Molecular mechanisms underlying obesity-related metabolic disorders have not been completely elucidated. Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily and are key metabolic regulators of the whole-body energy metabolism. Certain enzymes involved in carbohydrate and lipid metabolism are directly regulated by PPARs via their interaction with specific response elements in their gene promoters. Many food factors act as ligands of PPARs and regulate carbohydrate and lipid metabolism by regulating the activities of these nuclear receptors, leading to the attenuation of obesity-related metabolic disorders. In this review, we describe our current knowledge of the role of PPARs in the regulation of whole-body energy metabolism and several examples of food factors that act as ligands of PPARs, which may be useful in the management of obesity and the accompanying energy metabolism abnormalities.

Abbreviations: WAT: white adipose tissue; PPAR: Peroxisome proliferators-activated receptor; RXR: retinoid X receptors; mTORC1: mechanistic target of rapamycin complex 1; PPRE: PPAR-responsive regulatory elements; NAFLD: nonalcoholic fatty liver disease; LPL: lipoprotein lipase; FGF21: fibroblast growth factor 21; BAT: brown adipose tissue; UCP1: uncoupling protein 1; LPC(16:0): 1-palmitoyl lysophosphatidylcholine; C/EBP: CCAAT-enhancer binding proteins; STAT5A: signal transduction and activator of transcription 5A; APO apolipoptotein; CBP: cAMP response element-binding protein-binding protein; PGC1A: PPARγ coactivator protein 1a; HFD: high-fat diet; TG: triglyceride; VLDL: very low density lipoprotein; HDL: high density lipoprotein

Apo-12'-lycopenal, a Lycopene Metabolite, Promotes Adipocyte Differentiation via Peroxisome Proliferator-Activated Receptor γ Activation

Apo-lycopenals, lycopene metabolites produced by an initial cleavage by β,β-carotene-9',10'-oxygenase, exhibit diverse biologically active effects. In this study, we investigated the effect of apo-lycopenals on the activation of nuclear receptors involved in glucose and lipid metabolism. Only apo-12'-lycopenal exhibited selective and dose-dependent transactivation activity for peroxisome proliferator-activated receptor γ (PPARγ), whereas neither apo-6'- nor apo-8'-lycopenals displayed this activity ((7.83 ± 0.66)-, (1.32 ± 0.10)-, and (1.31 ± 0.37)-fold higher activity relative to control, respectively). Additionally, apo-12'-lycopenal promoted adipocyte differentiation of 3T3-L1 cells and subsequently increased the mRNA levels of PPARγ (a (2.36 ± 0.07)-fold increase relative to control; p < 0.01) and its target genes, as well as enhanced adiponectin secretion (a (3.25 ± 0.27)-fold increase relative to control; p < 0.01) and insulin-stimulated glucose uptake (1486 ± 85 pmol/well; p < 0.001) in 3T3-L1 cells. Our results indicated that apo-12'-lycopenal promoted adipocyte differentiation by direct binding and activation of PPARγ.

The Mevalonate Pathway Is Indispensable for Adipocyte Survival

The mevalonate pathway is essential for the synthesis of isoprenoids and cholesterol. Adipose tissue is known as a major site for cholesterol storage; however, the role of the local mevalonate pathway and its synthesized isoprenoids remains unclear. In this study, adipose-specific mevalonate pathway-disrupted (aKO) mice were generated through knockout of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase (HMGCR). aKO mice showed serious lipodystrophy accompanied with glucose and lipid metabolic disorders and hepatomegaly. These metabolic variations in aKO mice were dramatically reversed after fat transplantation. In addition, HMGCR-disrupted adipocytes exhibited loss of lipid accumulation and an increase of cell death, which were ameliorated by the supplementation of mevalonate and geranylgeranyl pyrophosphate but not farnesyl pyrophosphate and squalene. Finally, we found that apoptosis may be involved in adipocyte death induced by HMGCR down-regulation. Our findings indicate that the mevalonate pathway is essential for adipocytes and further suggest that this pathway is an important regulator of adipocyte turnover.

Food-derived regulatory factors against obesity and metabolic syndrome

Obesity is a key factor in metabolic syndrome. The study of metabolic syndrome focuses on the anti-weight gain properties of physiological mechanisms and food components. Abnormal energy metabolism is a major risk factor of metabolic syndrome. Chronic inflammation is a feature of obesity; cytokines from hypertrophied adipocytes cause inflammation in both adipose tissue and blood vessels, resulting in symptoms of metabolic syndrome. Tumor necrosis factor-α causes insulin resistance in adipocytes and regression of brown adipocytes, resulting in abnormal energy metabolism. Functional foods can serve as a strategy for prevention and treatment of obesity linked with metabolic processes in white and brown adipose tissues. Diet-induced thermogenesis caused by certain food components stimulates burning of stored fat within adipose tissues. A mechanistic understanding of dietary thermogenesis via the sympathetic nerve system will prove valuable for the development of precise strategies for the practical prevention of metabolic syndrome.

The hepatokine FGF21 is crucial for peroxisome proliferator-activated receptor-α agonist-induced amelioration of metabolic disorders in obese mice

Obesity causes excess fat accumulation in white adipose tissues (WAT) and also in other insulin-responsive organs such as the skeletal muscle, increasing the risk for insulin resistance, which can lead to obesity-related metabolic disorders. Peroxisome proliferator-activated receptor-α (PPARα) is a master regulator of fatty acid oxidation whose activator is known to improve hyperlipidemia. However, the molecular mechanisms underlying PPARα activator-mediated reduction in adiposity and improvement of metabolic disorders are largely unknown. In this study we investigated the effects of PPARα agonist (fenofibrate) on glucose metabolism dysfunction in obese mice. Fenofibrate treatment reduced adiposity and attenuated obesity-induced dysfunctions of glucose metabolism in obese mice fed a high-fat diet. However, fenofibrate treatment did not improve glucose metabolism in lipodystrophic A-Zip/F1 mice, suggesting that adipose tissue is important for the fenofibrate-mediated amelioration of glucose metabolism, although skeletal muscle actions could not be completely excluded. Moreover, we investigated the role of the hepatokine fibroblast growth factor 21 (FGF21), which regulates energy metabolism in adipose tissue. In WAT of WT mice, but not of FGF21-deficient mice, fenofibrate enhanced the expression of genes related to brown adipocyte functions, such as Ucp1, Pgc1a, and Cpt1b Fenofibrate increased energy expenditure and attenuated obesity, whole body insulin resistance, and adipocyte dysfunctions in WAT in high-fat-diet-fed WT mice but not in FGF21-deficient mice. These findings indicate that FGF21 is crucial for the fenofibrate-mediated improvement of whole body glucose metabolism in obese mice via the amelioration of WAT dysfunctions.

Geranylgeranyl pyrophosphate performs as an endogenous regulator of adipocyte function via suppressing the LXR pathway

Isoprenoids such as geranylgeranyl pyrophosphate (GGPP) influence various biological processes. Here we show that GGPP inhibits adipocyte differentiation via the liver X receptors (LXRs) pathway. Intracellular GGPP levels and GGPP synthase (Ggps) mRNA expression increases during adipocyte differentiation. Ggps expression also increases in white adipose tissue of obese mice. GGPP addition reduces the expression of adipogenic marker genes such as adipocyte fatty acid binding protein, peroxisome proliferator-activated receptor γ, and insulin-stimulated glucose uptake. Similarly, over-expressing Ggps inhibits adipocyte differentiation. In contrast, Ggps knockdown promotes adipocyte differentiation. Inhibition of adipocyte differentiation by GGPP was partially reduced by LXR agonist T0901317. Furthermore, Ggps knockdown up-regulates LXR target genes during adipocyte differentiation. These results suggest that GGPP may act as an endogenous regulator of adipocyte differentiation and maturation through a mechanism partially dependent on the LXR pathway.

Differential Regulation of Gene Expression by Cholesterol Biosynthesis Inhibitors That Reduce (Pravastatin) or Enhance (Squalestatin 1) Nonsterol Isoprenoid Levels in Primary Cultured Mouse and Rat Hepatocytes

Squalene synthase inhibitors (SSIs), such as squalestatin 1 (SQ1), reduce cholesterol biosynthesis but cause the accumulation of isoprenoids derived from farnesyl pyrophosphate (FPP), which can modulate the activity of nuclear receptors, including the constitutive androstane receptor (CAR), farnesoid X receptor, and peroxisome proliferator-activated receptors (PPARs). In comparison, 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (e.g., pravastatin) inhibit production of both cholesterol and nonsterol isoprenoids. To characterize the effects of isoprenoids on hepatocellular physiology, microarrays were used to compare orthologous gene expression from primary cultured mouse and rat hepatocytes that were treated with either SQ1 or pravastatin. Compared with controls, 47 orthologs were affected by both inhibitors, 90 were affected only by SQ1, and 51 were unique to pravastatin treatment (P < 0.05, ≥1.5-fold change). When the effects of SQ1 and pravastatin were compared directly, 162 orthologs were found to be differentially coregulated between the two treatments. Genes involved in cholesterol and unsaturated fatty acid biosynthesis were up-regulated by both inhibitors, consistent with cholesterol depletion; however, the extent of induction was greater in rat than in mouse hepatocytes. SQ1 induced several orthologs associated with microsomal, peroxisomal, and mitochondrial fatty acid oxidation and repressed orthologs involved in cell cycle regulation. By comparison, pravastatin repressed the expression of orthologs involved in retinol and xenobiotic metabolism. Several of the metabolic genes altered by isoprenoids were inducible by a PPARα agonist, whereas cytochrome P450 isoform 2B was inducible by activators of CAR. Our findings indicate that SSIs uniquely influence cellular lipid metabolism and cell cycle regulation, probably due to FPP catabolism through the farnesol pathway.

Benzyl butyl phthalate promotes adipogenesis in 3T3-L1 preadipocytes: A High Content Cellomics and metabolomic analysis

Benzyl butyl phthalate (BBP) has been known to induce developmental and reproductive toxicity. However, its association with dysregulation of adipogenesis has been poorly investigated. The present study aimed to examine the effect of BBP on the adipogenesis, and to elucidate the underlying mechanisms using the 3T3-L1 cells. The capacity of BBP to promote adipogenesis was evaluated by multiple staining approaches combined with a High Content Cellomics analysis. The dynamic changes of adipogenic regulatory genes and proteins were examined, and the metabolite profile was identified using GC/MC based metabolomic analysis. The High Content analysis showed BBP in contrast with Bisphenol A (BPA), a known environmental obesogen, increased lipid droplet accumulation in a similar dose-dependent manner. However, the size of the lipid droplets in BBP-treated cells was significantly larger than those in cells treated with BPA. BBP significantly induced mRNA expression of transcriptional factors C/EBPα and PPARγ, their downstream genes, and numerous adipogenic proteins in a dose and time-dependent manner. Furthermore, GC/MC metabolomic analysis revealed that BBP exposure perturbed the metabolic profiles that are associated with glyceroneogenesis and fatty acid synthesis. Altogether, our current study clearly demonstrates that BBP promoted the differentiation of 3T3-L1 through the activation of the adipogenic pathway and metabolic disturbance.

Nonsterol Isoprenoids Activate Human Constitutive Androstane Receptor in an Isoform-Selective Manner in Primary Cultured Mouse Hepatocytes

Our laboratory previously reported that accumulation of nonsterol isoprenoids following treatment with the squalene synthase inhibitor, squalestatin 1 (SQ1) markedly induced cytochrome P450 (CYP)2B1 mRNA and reporter activity in primary cultured rat hepatocytes, which was dependent on activation of the constitutive androstane receptor (CAR). The objective of the current study was to evaluate whether isoprenoids likewise activate murine CAR (mCAR) or one or more isoforms of human CAR (hCAR) produced by alternative splicing (SPTV, hCAR2; APYLT, hCAR3). We found that SQ1 significantly induced Cyp2b10 mRNA (∼3.5-fold) in primary hepatocytes isolated from both CAR-wild-type and humanized CAR transgenic mice, whereas the 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor pravastatin had no effect. In the absence of CAR, basal Cyp2b10 mRNA levels were reduced by 28-fold and the effect of SQ1 on Cyp2b10 induction was attenuated. Cotransfection with an expression plasmid for hCAR1, but not hCAR2 or hCAR3, mediated SQ1-induced CYP2B1 and CYP2B6 reporter activation in hepatocytes isolated from CAR-knockout mice. This effect was also observed following treatment with the isoprenoid trans,trans-farnesol. The direct agonist CITCO increased interaction of hCAR1, hCAR2, and hCAR3 with steroid receptor coactivator-1. However, no significant effect on coactivator recruitment was observed with SQ1, suggesting an indirect activation mechanism. Further results from an in vitro ligand binding assay demonstrated that neither farnesol nor other isoprenoids are direct ligands for hCAR1. Collectively, our findings demonstrate that SQ1 activates CYP2B transcriptional responses through farnesol metabolism in an hCAR1-dependent manner. Further, this effect probably occurs through an indirect mechanism.

Trans, trans-farnesol as a mevalonate-derived inducer of murine 3T3-F442A pre-adipocyte differentiation

Based on our finding that depletion of mevalonate-derived metabolites inhibits adipocyte differentiation, we hypothesize that trans, trans-farnesol (farnesol), a mevalonate-derived sesquiterpene, induces adipocyte differentiation. Farnesol dose-dependently (25-75 μmol/L) increased intracellular triglyceride content of murine 3T3-F442A pre-adipocytes measured by AdipoRed™ Assay and Oil Red-O staining. Concomitantly, farnesol dose-dependently increased glucose uptake and glucose transport protein 4 (GLUT4) expression without affecting cell viability. Furthermore, quantitative real-time polymerase chain reaction and Western blot showed that farnesol increased the mRNA and protein levels of peroxisome proliferator-activated receptor γ (PPARγ), a key regulator of adipocyte differentiation, and the mRNA levels of PPARγ-regulated fatty acid-binding protein 4 and adiponectin; in contrast, farnesol downregulated Pref-1 gene, a marker of pre-adipocytes. GW9662 (10 µmol/L), an antagonist of PPARγ, reversed the effects of farnesol on cellular lipid content, suggesting that PPARγ signaling pathway may mediate the farnesol effect. Farnesol (25-75 μmol/L) did not affect the mRNA level of 3-hydroxy-3-methylglutaryl coenzyme A reductase, the rate-limiting enzyme in the mevalonate pathway. Farnesol may be the mevalonate-derived inducer of adipocyte differentiation and potentially an insulin sensitizer via activation of PPARγ and upregulation of glucose uptake.

Proinflammatory cytokine interleukin-1β suppresses cold-induced thermogenesis in adipocytes

In this study, we investigated the effects of interleukin-1β (IL-1β), a typical proinflammatory cytokine on the β-adrenoreceptor-stimulated induction of uncoupling protein 1 (UCP1) expression in adipocytes. IL-1β mRNA expression levels were upregulated in white adipose tissues of obese mice and in RAW264.7 macrophages under conditions designed to mimic obese adipose tissue. Isoproterenol-stimulated induction of UCP1 mRNA expression was significantly inhibited in C3H10T1/2 adipocytes by conditioned medium from lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages in comparison with control conditioned medium. This inhibition was significantly attenuated in the presence of recombinant IL-1 receptor antagonist and IL-1β antibody, suggesting that activated macrophage-derived IL-1β is an important cytokine for inhibition of β-adrenoreceptor-stimulated UCP1 induction in adipocytes. IL-1β suppressed isoproterenol-induced UCP1 mRNA expression in C3H10T1/2 adipocytes, and this effect was partially but significantly abrogated by inhibition of extracellular signal-regulated kinase (ERK). IL-1β also suppressed the isoproterenol-induced activation of the UCP1 promoter and transcription factors binding to the cAMP response element. Moreover, intraperitoneal administration of IL-1β suppressed cold-induced UCP1 expression in adipose tissues. These findings suggest that IL-1β upregulated in obese adipose tissues suppresses β-adrenoreceptor-stimulated induction of UCP1 expression through ERK activation in adipocytes.

Transcriptional Regulation of Cytosolic Sulfotransferase 1C2 by Intermediates of the Cholesterol Biosynthetic Pathway in Primary Cultured Rat Hepatocytes

Cytosolic sulfotransferase 1C2 (SULT1C2) is expressed in the kidney, stomach, and liver of rats; however, the mechanisms regulating expression of this enzyme are not known. We evaluated transcriptional regulation of SULT1C2 by mevalonate (MVA)-derived intermediates in primary cultured rat hepatocytes using several cholesterol synthesis inhibitors. Blocking production of mevalonate with the 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor pravastatin (30 μM), reduced SULT1C2 mRNA content by ∼40% whereas the squalene synthase inhibitor squalestatin (SQ1, 0.1 μM), which causes accumulation of nonsterol isoprenoids, increased mRNA content by 4-fold. Treatment with MVA (10 mM) strongly induced SULT1C2 mRNA by 12-fold, and this effect was blocked by inhibiting squalene epoxidase but not by more distal cholesterol inhibitors, indicating the effects of MVA are mediated by postsqualene metabolites. Using rapid amplification of cDNA ends (RACE), we characterized the 5' end of SULT1C2 mRNA and used this information to generate constructs for promoter analysis. SQ1 and MVA increased reporter activity by ∼1.6- and 3-fold, respectively, from a construct beginning 49 base pairs (bp) upstream from the longest 5'-RACE product (-3140:-49). Sequence deletions from this construct revealed a hepatocyte nuclear factor 1 (HNF1) element (-2558), and mutation of this element reduced basal (75%) and MVA-induced (30%) reporter activity and attenuated promoter activation following overexpression of HNF1α or 1β. However, the effects of SQ1 were localized to a more proximal promoter region (-281:-49). Collectively, our findings demonstrate that cholesterol biosynthetic intermediates influence SULT1C2 expression in rat primary hepatocytes. Further, HNF1 appears to play an important role in mediating basal and MVA-induced SULT1C2 transcription.

Promoting effect of triterpenoid compound from Agrimonia pilosa Ledeb on preadipocytes differentiation via up-regulation of PPARγ expression

Background:

Agrimonia Pilosa Ledeb (APL), a traditional Chinese medicine, has been reported a variety of biological activities, including treating T2DM.

Objective:

Triterpenoid compound (TC) was collected from APL. The aim of this study was to investigate the effects of TC on 3T3-L1 preadipocytes differentiation and genes related to differentiation and IR.

Materials and Methods:

Column chromatography was used to collect TC from ALP. 3T3-L1 cell differentiation was induced typically in the presence of various concentrations of TC or pioglitazone. Oil red O staining and measurement of intracellular TG content were performed on the seventh day of differentiation. Then quantitative polymerase chain reaction (Q-PCR) was used to test the expressions of three transcription factors (PPARγ, CCAAT enhancer binding protein-α (C/EBP-α), and sterol regulatory element-binding protein 1 (SREBP-1)) and the target genes of PPARγ including glucose transporter (GLUT4), lipoprotein lipase (LPL), fat acid binding protein (AP2), and adiponectin in 3T3-L1 cells.

Results:

At the concentration of 5, 25 and 125 μg/mL, TC significantly promoted triglyceride accumulation. Further study showed that TC could promote the expression of PPARγ, C/EBPα and ADD1/SREBP1 significantly at 125 μg/mL. As for downstream genes controlled by PPARγ, TC at 25 and 125 μg/mL could significantly promote the expression of GLUT4 and adiponectin. However, the expression of aP2 related to lipid metabolism and adiposity in the TC group was significantly lower than that in the pioglitazone group.

Conclusion:

TC could promote preadipocytes differentiation through activating PPARγ and downstream controlled genes. TC has the ideal insulin sensitization with lower adipogenic action than classical TZDs in vitro. So TC from Agrimonia Pilosa Ledeb has a good prospect as a natural drug for IR and T2DM.

Metabolomics reveal 1-palmitoyl lysophosphatidylcholine production by peroxisome proliferator-activated receptor α

PPARα is well known as a master regulator of lipid metabolism. PPARα activation enhances fatty acid oxidation and decreases the levels of circulating and cellular lipids in obese diabetic patients. Although PPARα target genes are widely known, little is known about the alteration of plasma and liver metabolites during PPARα activation. Here, we report that metabolome analysis-implicated upregulation of many plasma lysoGP species during bezafibrate (PPARα agonist) treatment. In particular, 1-palmitoyl lysophosphatidylcholine [LPC(16:0)] is increased by bezafibrate treatment in both plasma and liver. In mouse primary hepatocytes, the secretion of LPC(16:0) increased on PPARα activation, and this effect was attenuated by PPARα antagonist treatment. We demonstrated that Pla2g7 gene expression levels in the murine hepatocytes were increased by PPARα activation, and the secretion of LPC(16:0) was suppressed by Pla2g7 siRNA treatment. Interestingly, LPC(16:0) activates PPARα and induces the expression of PPARα target genes in hepatocytes. Furthermore, we showed that LPC(16:0) has the ability to recover glucose uptake in adipocytes induced insulin resistance. These results reveal that LPC(16:0) is induced by PPARα activation in hepatocytes; LPC(16:0) contributes to the upregulation of PPARα target genes in hepatocytes and the recovery of glucose uptake in insulin-resistant adipocytes.

13-Oxo-9(Z),11(E),15(Z)-octadecatrienoic acid activates peroxisome proliferator-activated receptor γ in adipocytes

Peroxisome proliferator-activated receptor (PPAR)γ is expressed in adipose tissue and plays a key role in the regulation of adipogenesis. PPARγ activators are known to have potent antihyperglycemic activity and are used to treat insulin resistance associated with diabetes. Therefore, many natural and synthetic agonists of PPARγ are used in the treatment of glucose disorders. In the present study, we found that 13-oxo-9(Z),11(E),15(Z)-octadecatrienoic acid (13-oxo-OTA), a linolenic acid derivative, is present in the extract of tomato (Solanum lycopersicum), Mandarin orange (Citrus reticulata), and bitter gourd (Momordica charantia). We also found that 13-oxo-OTA activated PPARγ and induced the mRNA expression of PPARγ target genes in adipocytes, thereby promoting differentiation. Furthermore, 13-oxo-OTA induced secretion of adiponectin and stimulated glucose uptake in adipocytes. To our knowledge, this is the first study to report that 13-oxo-OTA induces adipogenesis through PPARγ activation and to present 13-oxo-OTA as a valuable food-derived compound that may be applied in the management of glucose metabolism disorders.

Natural product agonists of peroxisome proliferator-activated receptor gamma (PPARγ): a review

Agonists of the nuclear receptor PPARγ are therapeutically used to combat hyperglycaemia associated with the metabolic syndrome and type 2 diabetes. In spite of being effective in normalization of blood glucose levels, the currently used PPARγ agonists from the thiazolidinedione type have serious side effects, making the discovery of novel ligands highly relevant. Natural products have proven historically to be a promising pool of structures for drug discovery, and a significant research effort has recently been undertaken to explore the PPARγ-activating potential of a wide range of natural products originating from traditionally used medicinal plants or dietary sources. The majority of identified compounds are selective PPARγ modulators (SPPARMs), transactivating the expression of PPARγ-dependent reporter genes as partial agonists. Those natural PPARγ ligands have different binding modes to the receptor in comparison to the full thiazolidinedione agonists, and on some occasions activate in addition PPARα (e.g. genistein, biochanin A, sargaquinoic acid, sargahydroquinoic acid, resveratrol, amorphastilbol) or the PPARγ-dimer partner retinoid X receptor (RXR; e.g. the neolignans magnolol and honokiol). A number of in vivo studies suggest that some of the natural product activators of PPARγ (e.g. honokiol, amorfrutin 1, amorfrutin B, amorphastilbol) improve metabolic parameters in diabetic animal models, partly with reduced side effects in comparison to full thiazolidinedione agonists. The bioactivity pattern as well as the dietary use of several of the identified active compounds and plant extracts warrants future research regarding their therapeutic potential and the possibility to modulate PPARγ activation by dietary interventions or food supplements.

Gamma-tocotrienol attenuates high-fat diet-induced obesity and insulin resistance by inhibiting adipose inflammation and M1 macrophage recruitment

BACKGROUND AND OBJECTIVE

We have previously demonstrated that gamma tocotrienol (γT3) potently inhibits adipocyte hyperplasia in human adipose-derived stem cells (hASCs). In this study, our objective was to investigate the γT3 effects on early-onset obesity, inflammation and insulin resistance in vivo.

METHODS

Young C57BL/6J mice were fed a high-fat (HF) diet supplemented with 0.05% γT3 for 4 weeks. The concentrations of γT3 in plasma and adipose tissue were measured using high-performance liquid chromatography. Effects of γT3 on body weight gain, adipose volume, plasma levels of fasting glucose, insulin (enzyme-linked immunosorbent assay (ELISA)), proinflammatory cytokines (mouse cytokine array), insulin signaling (western blotting) and gene expression (quantitative real-time PCR, qPCR) in the liver and adipose tissue were examined. Influences of γT3 on [3H]-2-deoxyglucose uptake and lipopolysaccharide (LPS)-mediated NFκB signaling (western blotting) were assessed in hASCs. Effects of γT3 on macrophage M1/M2 activation were investigated using qPCR in mouse bone marrow-derived macrophages.

RESULTS

After a 4-week treatment, γT3 accumulated in adipose tissue and reduced HF diet-induced weight gain in epididymal fat, mesenteric fat and the liver. Compared with HF diet-fed mice, HF+γT3-fed mice were associated with (1) decreased plasma levels of fasting glucose, insulin and proinflammatory cytokines, (2) improved glucose tolerance and (3) enhanced insulin signaling in adipose tissue. There were substantial decreases in macrophage specific markers, and monocyte chemoattractant protein-1, indicating that γT3 reduced the recruitment of adipose tissue macrophages (ATMs). In addition, γT3 treatment in human adipocytes resulted in (1) activation of insulin-stimulated glucose uptake and (2) a significant suppression of MAP kinase and NFκB activation. In parallel, γT3 treatment led to a reduction of LPS-mediated M1 macrophage polarization.

CONCLUSION

Our results demonstrated that γT3 ameliorates HF diet-mediated obesity and insulin resistance by inhibiting systemic and adipose inflammation, as well as ATM recruitment.

CMHX008, a novel peroxisome proliferator-activated receptor γ partial agonist, enhances insulin sensitivity in vitro and in vivo

The peroxisome proliferator-activated receptor γ (PPARγ) plays an important role in adipocyte differentiation and insulin sensitivity. Its ligand rosiglitazone has anti-diabetic effect but is frequently accompanied with some severe unwanted effects. The aim of the current study was to compare the anti-diabetic effect of CMHX008, a novel thiazolidinedione-derivative, with rosiglitazone. A luciferase assay was used to evaluate in vitro PPARγ activation. 3T3-L1 cells were used to examine adipocyte differentiation. High fat diet (HFD) mice were used to examine in vivo insulin sensitivity. The mRNA levels were evaluated by real-time RT-PCR. Serum biochemical and hormonal variables were assessed using a clinical chemistry analyser. CMHX008 displayed a moderate PPARγ agonist activity, and promoted 3T3-L1 preadipocyte differentiation with lower activity than rosiglitazone. CMHX008 regulated the expression of PPARγ target genes in a different manner from rosiglitazone. CMHX008 increased the expression and secretion of adiponectin with the similar efficacy as rosiglitazone, but only 25% as potent as rosiglitazone for the induction of adipocyte fatty acid binding protein. Treatment of CMHX008 and rosiglitazone protected mice from high fat diet (HFD)-induced glucose intolerance, hyperinsulinemia and inflammation. CMHX008 reduced the mRNA expression of M1 macrophage markers, and significantly increased the expressions of M2 markers. In conclusion, CMHX008 shared the comparable insulin-sensitizing effects as rosiglitazone with lower adipogenic capacity and might potentially be developed into an effective agent for the treatment of diabetes and metabolic disorders.

Statin treatment and new-onset diabetes: a review of proposed mechanisms

New-onset diabetes has been observed in clinical trials and meta-analyses involving statin therapy. To explain this association, three major mechanisms have been proposed and discussed in the literature. First, certain statins affect insulin secretion through direct, indirect or combined effects on calcium channels in pancreatic β-cells. Second, reduced translocation of glucose transporter 4 in response to treatment results in hyperglycemia and hyperinsulinemia. Third, statin therapy decreases other important downstream products, such as coenzyme Q10, farnesyl pyrophosphate, geranylgeranyl pyrophosphate, and dolichol; their depletion leads to reduced intracellular signaling. Other possible mechanisms implicated in the effect of statins on new-onset diabetes are: statin interference with intracellular insulin signal transduction pathways via inhibition of necessary phosphorylation events and reduction of small GTPase action; inhibition of adipocyte differentiation leading to decreased peroxisome proliferator activated receptor gamma and CCAAT/enhancer-binding protein which are important pathways for glucose homeostasis; decreased leptin causing inhibition of β-cells proliferation and insulin secretion; and diminished adiponectin levels. Given that the magnitude of the risk of new-onset diabetes following statin use remains to be fully clarified and the well-established beneficial effect of statins in reducing cardiovascular risk, statins remain the first-choice treatment for prevention of CVD. Elucidation of the mechanisms underlying the development of diabetes in association with statin use may help identify novel preventative or therapeutic approaches to this problem and/or help design a new generation statin without such side-effects.

Integrated analysis of transcript-level regulation of metabolism reveals disease-relevant nodes of the human metabolic network

Metabolic diseases and comorbidities represent an ever-growing epidemic where multiple cell types impact tissue homeostasis. Here, the link between the metabolic and gene regulatory networks was studied through experimental and computational analysis. Integrating gene regulation data with a human metabolic network prompted the establishment of an open-sourced web portal, IDARE (Integrated Data Nodes of Regulation), for visualizing various gene-related data in context of metabolic pathways. Motivated by increasing availability of deep sequencing studies, we obtained ChIP-seq data from widely studied human umbilical vein endothelial cells. Interestingly, we found that association of metabolic genes with multiple transcription factors (TFs) enriched disease-associated genes. To demonstrate further extensions enabled by examining these networks together, constraint-based modeling was applied to data from human preadipocyte differentiation. In parallel, data on gene expression, genome-wide ChIP-seq profiles for peroxisome proliferator-activated receptor (PPAR) γ, CCAAT/enhancer binding protein (CEBP) α, liver X receptor (LXR) and H3K4me3 and microRNA target identification for miR-27a, miR-29a and miR-222 were collected. Disease-relevant key nodes, including mitochondrial glycerol-3-phosphate acyltransferase (GPAM), were exposed from metabolic pathways predicted to change activity by focusing on association with multiple regulators. In both cell types, our analysis reveals the convergence of microRNAs and TFs within the branched chain amino acid (BCAA) metabolic pathway, possibly providing an explanation for its downregulation in obese and diabetic conditions.

Mevalonate deprivation mediates the impact of lovastatin on the differentiation of murine 3T3-F442A preadipocytes

The statins competitively inhibit 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase activity and consequently the synthesis of mevalonate. The use of statins is associated with insulin resistance, presumably due to the impaired differentiation and diminished glucose utilization of adipocytes. We hypothesize that mevalonate is essential to adipocyte differentiation and adipogenic gene expression. Adipo-Red assay and Oil Red O staining showed that an eight-day incubation with 0-2.5 µmol/L lovastatin dose-dependently reduced the intracellular triglyceride content of murine 3T3-F442A adipocytes. Concomitantly, lovastatin downregulated the expression of peroxisome proliferator-activated receptor γ (Pparγ), leptin (Lep), fatty acid binding protein 4 (Fabp4), and adiponectin (AdipoQ) as measured by quantitative real-time polymerase chain reaction (real-time qPCR). The expression of sterol regulatory element binding protein 1 (Srebp-1), a transcriptional regulator of Pparγ and Lep genes, was also suppressed by lovastatin. Western-blot showed that lovastatin reduced the level of CCAAT/enhancer binding protein α (C/EBPα) while inducing a compensatory over-expression of HMG CoA reductase. The impact of lovastatin on intracellular triglyceride content and expression of the adipogenic genes was reversed by supplemental mevalonate. Mevalonate-derived metabolites have essential roles in promoting adipogenic gene expression and adipocyte differentiation.

Bixin activates PPARα and improves obesity-induced abnormalities of carbohydrate and lipid metabolism in mice

Peroxisome proliferator-activated receptor α (PPARα) is a ligand-activated transcription factor that regulates the expression of the genes involved in fatty acid oxidation. PPARα activators induce fatty acid oxidation in the liver, thereby improving lipid and carbohydrate metabolism in obese mice. In this study, the dietary cis-carotenoids bixin and norbixin, which are commonly used in the food coloring industry, were found to activate PPARα by luciferase reporter assays using GAL4/PPARα chimeric and full-length PPARα systems. Treatment with bixin and norbixin induced the mRNA expression of PPARα target genes involved in fatty acid oxidation in PPARα-expressing HepG2 hepatocytes. In obese KK-Ay mice, bixin treatment suppressed the development of hyperlipidemia and hepatic lipid accumulation. In the livers of bixin-treated mice, the mRNA levels of PPARα target genes related to fatty acid oxidation were up-regulated. Moreover, bixin treatment also improved obesity-induced dysfunctions of carbohydrate metabolism, such as hyperglycemia, hyperinsulinemia, and hypoadiponectinemia. Glucose tolerance test and insulin tolerance test revealed that glucose intolerance and insulin resistance in KK-Ay obese mice were attenuated by the treatment with bixin. These results indicate that bixin acts as a food-derived agonist of PPARα, and bixin treatment is useful for the management of obesity-induced metabolic dysfunctions in mice.

Inhibition of lipid phosphate phosphatase activity by VPC32183 suppresses the ability of diacylglycerol pyrophosphate to activate ERK(1/2) MAP kinases

The lipidic metabolite, diacylglycerol pyrophosphate (DGPP), in its dioctanoyl form (DGPP 8:0), has been described as an antagonist for mammalian lysophosphatidic acid (LPA) receptors LPA1 and LPA3. In this study we show that DGPP 8:0 does not antagonize LPA dependent activation of ERK(1/2) MAP kinases but strongly stimulated them in various mammalian cell lines. LPA and DGPP 8:0 stimulation of ERK(1/2) occurred through different pathways. The DGPP 8:0 effect appeared to be dependent on PKC, Raf and MEK but was insensitive to pertussis toxin and did not involve G protein activation. Finally we showed that DGPP 8:0 effect on ERK(1/2) was dependent on its dephosphorylation by a phosphatase activity sharing lipid phosphate phosphatase properties. The inhibition of this phosphatase activity by VPC32183, a previously characterized LPA receptor antagonist, blocked the DGPP 8:0 effect on ERK(1/2) activation. Moreover, down-regulation of lipid phosphate phosphatase 1 (LPP1) expression by RNA interference technique also reduced DGPP 8:0-induced ERK(1/2) activation. Consistently, over expression of LPP1 in HEK293 cells increases DGPP 8:0 hydrolysis and this increased activity was inhibited by VPC32183. In conclusion, DGPP 8:0 does not exert its effect by acting on a G protein coupled receptor, but through its dephosphorylation by LPP1, generating dioctanoyl phosphatidic acid which in turn activates PKC. These results suggest that LPP1 could have a positive regulatory function on cellular signaling processes such as ERK(1/2) activation.

The dynamic roles of intracellular lipid droplets: from archaea to mammals

During the past decade, there has been a paradigm shift in our understanding of the roles of intracellular lipid droplets (LDs). New genetic, biochemical and imaging technologies have underpinned these advances, which are revealing much new information about these dynamic organelles. This review takes a comparative approach by examining recent work on LDs across the whole range of biological organisms from archaea and bacteria, through yeast and Drosophila to mammals, including humans. LDs probably evolved originally in microorganisms as temporary stores of excess dietary lipid that was surplus to the immediate requirements of membrane formation/turnover. LDs then acquired roles as long-term carbon stores that enabled organisms to survive episodic lack of nutrients. In multicellular organisms, LDs went on to acquire numerous additional roles including cell- and organism-level lipid homeostasis, protein sequestration, membrane trafficking and signalling. Many pathogens of plants and animals subvert their host LD metabolism as part of their infection process. Finally, malfunctions in LDs and associated proteins are implicated in several degenerative diseases of modern humans, among the most serious of which is the increasingly prevalent constellation of pathologies, such as obesity and insulin resistance, which is associated with metabolic syndrome.

Isoprenoid is a perfect fit for fat factor

In humans, there are 48 members of the superfamily of nuclear receptors. These ligand-activated transcription factors help to integrate our growth, reproduction and metabolism via environmental, nutritional and intrinsic cues. It is therefore not surprising that nuclear receptors are commonly used as drug targets. However, perhaps in the rush to discover new drugs that target these receptors, we sometimes lose sight of their 'real' physiological ligands. In this issue of the Biochemical Journal Goto et al. present evidence that the isoprenoid FPP (farnesyl pyrophosphate) may be a bona fide ligand for the master controller of adipocyte differentiation PPARγ (peroxisome-proliferator-activated receptor γ). This work has wide-ranging implications not only for obesity and diabetes, but also for osteoporosis and the control of circadian rhythms in which PPARγ also plays an important role.