Suppression of adipocyte differentiation by aldo-keto reductase 1B3 acting as prostaglandin F2alpha synthase

An Investigation of the Saccharides Profile and Metabolic Gene Expression in Muskrat Scented Glands in Different Secretion Seasons

The adult male muskrat has a pair of scented glands, which show clear seasonal changes in their developmental status between the secretion season and non-secretion season. During the secretion season, the scented glands are much larger than in the non-secretion season, with the metabolism of glandular cells increasing and a large amount of musk being produced. In this work, the blood, musk, and scented gland tissue were collected from three healthy adult male muskrats during secretion season (September). And the blood and scented gland tissue from another three healthy adult male muskrats during the non-secretion season (November) were also sampled. The saccharides from blood and musk were detected by liquid chromatography-mass spectrometry (LC-MS), indicating the saccharides are concentrated in the scented glands during the secretion season. What is more, transcriptome analysis was employed to investigate the expression patterns of saccharides' pathways, suggesting some saccharides' metabolism-related genes undergo significant seasonal changes. Above all, scented gland saccharides' metabolism displays seasonal differences, and the enhancement in saccharides' metabolic activity during the secretion phase maintains glandular proliferation and secretion function.

Cancer to Cataracts: The Mechanistic Impact of Aldo-Keto Reductases in Chronic Diseases

Aldo-keto reductases (AKRs) are a superfamily of promiscuous enzymes that have been chiseled by evolution to act as catalysts for numerous regulatory pathways in humans. However, they have not lost their promiscuity in the process, essentially making them a double-edged sword. The superfamily is involved in multiple metabolic pathways and are linked to chronic diseases such as cataracts, diabetes, and various cancers. Unlike other detoxifying enzymes such as cytochrome P450s (CYP450s), short-chain dehydrogenases (SDRs), and medium-chain dehydrogenases (MDRs), that participate in essential pathways, AKRs are more widely distributed and have members with interchangeable functions. Moreover, their promiscuity is ubiquitous across all species and participates in the resistance of pathogenic microbes. Moreover, the introduction of synthetic substrates, such as synthetic molecules and processed foods, results in unwanted "toxification" due to enzyme promiscuity, leading to chronic diseases.

PPARγ regulates lipid metabolism and viability of sheep trophoblast cells

Peroxisome proliferator-activated receptor γ (PPARγ) is highly expressed in trophoblast tissues in pregnancy during which the protein participates in diverse events, including embryo implantation and placental formation. However, little is known about the role of PPARγ in embryonic development. This study investigated the function of PPARγ in sheep trophoblast cells. The coding sequence of sheep PPARγ encoded 475 amino acids and included one synonymou mutation compared with the sheep reference sequence for PPARγ. The PPARγ protein was localized in the nucleus and cytoplasm of sheep trophoblasts. The relative expression of PPARγ was elevated in cells treated with rosiglitazone and reduced following administration of GW9662. Activation of PPARγ promoted cell proliferation and mobility, but inhibited apoptosis. In addition, stimulation of PPARγ promoted the expression of lipid metabolism-related genes FABP4 and PLIN2. The expression of prostaglandin metabolism-related genes PLA2G4A, PTGS2 and PTGES also was upregulated significantly in trophoblast cells when PPARγ was activated. In contrast, activation of PPARγ did not impact expression of the prostaglandin-related genes PGFS and SLCO2A1. At the same time, activation of PPARγ activity increased the ratio of PGE2 to PGF2α. Furthermore, fluorescence labelling showed that the numbers of cell lipid droplets increased after stimulation of PPARγ activity, but decreased when PPARγ was inhibited. In conclusion, PPARγ is critical for the regulation of lipid metabolism and prostaglandin synthesis and secretion in sheep trophoblast cells and also has a potent effect on cell proliferation and viability.

Droplet Digital PCR Is a Novel Screening Method Identifying Potential Cardiac G-Protein-Coupled Receptors as Candidate Pharmacological Targets in a Rat Model of Pressure-Overload-Induced Cardiac Dysfunction

The identification of novel drug targets is needed to improve the outcomes of heart failure (HF). G-protein-coupled receptors (GPCRs) represent the largest family of targets for already approved drugs, thus providing an opportunity for drug repurposing. Here, we aimed (i) to investigate the differential expressions of 288 cardiac GPCRs via droplet digital PCR (ddPCR) and bulk RNA sequencing (RNAseq) in a rat model of left ventricular pressure-overload; (ii) to compare RNAseq findings with those of ddPCR; and (iii) to screen and test for novel, translatable GPCR drug targets in HF. Male Wistar rats subjected to transverse aortic constriction (TAC, n = 5) showed significant systolic dysfunction vs. sham operated animals (SHAM, n = 5) via echocardiography. In TAC vs. SHAM hearts, RNAseq identified 69, and ddPCR identified 27 significantly differentially expressed GPCR mRNAs, 8 of which were identified using both methods, thus showing a correlation between the two methods. Of these, Prostaglandin-F2α-receptor (Ptgfr) was further investigated and localized on cardiomyocytes and fibroblasts in murine hearts via RNA-Scope. Antagonizing Ptgfr via AL-8810 reverted angiotensin-II-induced cardiomyocyte hypertrophy in vitro. In conclusion, using ddPCR as a novel screening method, we were able to identify GPCR targets in HF. We also show that the antagonism of Ptgfr could be a novel target in HF by alleviating cardiomyocyte hypertrophy.

Eicosapentaenoic Acid Induces the Inhibition of Adipogenesis by Reducing the Effect of PPARγ Activator and Mediating PKA Activation and Increased COX-2 Expression in 3T3-L1 Cells at the Differentiation Stage

Obesity has received increasing attention in recent years because it is a factor in the development of non-communicable diseases. The current study aimed to analyze how representative fatty acids (FAs) such as palmitic acid, stearic acid, oleic acid, α-linolenic acid (ALA), and eicosapentaenoic acid (EPA) affected adipogenesis when/if introduced at the differentiation stage of 3T3-L1 cell culture. These FAs are assumed to be potentially relevant to the progression or prevention of obesity. EPA added during the differentiation stage reduced intracellular triacylglycerol (TAG) accumulation, as well as the expression of the established adipocyte-specific marker genes, during the maturation stage. However, no other FAs inhibited intracellular TAG accumulation. Coexistence of Δ12-prostaglandin J2, a peroxisome proliferator-activated receptor γ activator, with EPA during the differentiation stage partially attenuated the inhibitory effect of EPA on intracellular TAG accumulation. EPA increased cyclooxygenase-2 (COX-2) expression and protein kinase A (PKA) activity at the differentiation stage, which could explain the inhibitory actions of EPA. Taken together, exposure of preadipocytes to EPA only during the differentiation stage may be sufficient to finally reduce the mass of white adipose tissue through increasing COX-2 expression and PKA activity.

Prostaglandin D2 Added during the Differentiation of 3T3-L1 Cells Suppresses Adipogenesis via Dysfunction of D-Prostanoid Receptor P1 and P2

We previously reported that the addition of prostaglandin, (PG)D₂, and its chemically stable analog, 11-deoxy-11-methylene-PGD₂ (11d-11m-PGD₂), during the maturation phase of 3T3-L1 cells promotes adipogenesis. In the present study, we aimed to elucidate the effects of the addition of PGD₂ or 11d-11m-PGD₂ to 3T3-L1 cells during the differentiation phase on adipogenesis. We found that both PGD₂ and 11d-11m-PGD₂ suppressed adipogenesis through the downregulation of peroxisome proliferator-activated receptor gamma (PPARγ) expression. However, the latter suppressed adipogenesis more potently than PGD₂, most likely because of its higher resistance to spontaneous transformation into PGJ₂ derivatives. In addition, this anti-adipogenic effect was attenuated by the coexistence of an IP receptor agonist, suggesting that the effect depends on the intensity of the signaling from the IP receptor. The D-prostanoid receptors 1 (DP1) and 2 (DP2, also known as a chemoattractant receptor-homologous molecule expressed on Th2 cells) are receptors for PGD₂. The inhibitory effects of PGD₂ and 11d-11m-PGD₂ on adipogenesis were slightly attenuated by a DP2 agonist. Furthermore, the addition of PGD₂ and 11d-11m-PGD₂ during the differentiation phase reduced the DP1 and DP2 expression during the maturation phase. Overall, these results indicated that the addition of PGD₂ or 11d-11m-PGD₂ during the differentiation phase suppresses adipogenesis via the dysfunction of DP1 and DP2. Therefore, unidentified receptor(s) for both molecules may be involved in the suppression of adipogenesis.

Arachidonic Acid Added during the Differentiation Phase of 3T3-L1 Cells Exerts Anti-Adipogenic Effect by Reducing the Effects of Pro-Adipogenic Prostaglandins

A linoleic acid (LA) metabolite arachidonic acid (AA) added to 3T3-L1 cells is reported to suppress adipogenesis. The purpose of the present study aimed to clarify the effects of AA added during the differentiation phase, including adipogenesis, the types of prostaglandins (PG)s produced, and the crosstalk between AA and the PGs produced. Adipogenesis was inhibited by AA added, while LA did not. When AA was added, increased PGE₂ and PGF_2α production, unchanged Δ¹²-PGJ₂ production, and reduced PGI₂ production were observed. Since the decreased PGI₂ production was reflected in decreased CCAAT/enhancer-binding protein-β (C/EBPβ) and C/EBPδ expression, we expected that the coexistence of PGI₂ with AA would suppress the anti-adipogenic effects of AA. However, the coexistence of PGI₂ with AA did not attenuate the anti-adipogenic effects of AA. In addition, the results were similar when Δ¹²-PGJ₂ coexisted with AA. Taken together, these results indicated that the metabolism of ingested LA to AA is necessary to inhibit adipogenesis and that exposure of AA to adipocytes during only the differentiation phase is sufficient. As further mechanisms for suppressing adipogenesis, AA was found not only to increase PGE₂ and PGF_2α and decrease PGI₂ production but also to abrogate the pro-adipogenic effects of PGI₂ and Δ¹²-PGJ₂.

The biological actions of prostanoids in adipose tissue in physiological and pathophysiological conditions

Adipose tissue has been established as an endocrine organ that plays an important role in maintaining metabolic homeostasis. Adipose tissue releases several bioactive molecules called adipokines. Inflammation, dysregulation of adipokine synthesis, and secretion are observed in obesity and related diseases and cause adipose tissue dysfunction. Prostanoids, belonging to the eicosanoid family of lipid mediators, can be synthesized in adipose tissue and play a critical role in adipose tissue biology. In this review, we summarized the current knowledge regarding the interaction of prostanoids with adipokines, the expression of prostanoid receptors, and prostanoid synthase enzymes in adipose tissues in health and disease. Furthermore, the involvement of prostanoids in the physiological function or dysfunction of adipose tissue including inflammation, lipolysis, adipogenesis, thermogenesis, browning of adipocytes, and vascular tone regulation was also discussed by examining studies using pharmacological approaches or genetically modified animals for prostanoid receptors/synthase enzymes. Overall, the present review provides a perspective on the evidence from literature regarding the biological effects of prostanoids in adipose tissue. Among prostanoids, prostaglandin E2 (PGE₂) is prominent in regards to its substantial role in both adipose tissue physiology and pathophysiology. Targeting prostanoids may serve as a potential therapeutic strategy for preventing or treating obesity and related diseases.

Effects of PPAR-γ and RXR-α on mouse meibomian gland epithelial cells during inflammation induced by latanoprost

The purpose of this study is to investigate the effects of latanoprost on the secretion of cytokines and chemokines from meibomian gland epithelial cells, and to evaluate the modulation of peroxisome proliferator-activated receptor γ (PPAR-γ) and retinoid X receptor α (RXR-α) during latanoprost-induced inflammation. Mouse meibomian gland epithelial cells were cultured in proliferation and differentiation medium, respectively. Cells were exposed to latanoprost, rosiglitazone (PPAR-γ agonist), or LG100268 (RXR-α agonist), respectively. The expression of IL-6, IL-1β, TNF-α, MMP-9, MCP-1, and CCL-5 were detected by real-time PCR and ELISA. The effect of latanoprost, rosiglitazone, LG100268, and inflammatory cytokines on the differentiation of meibocyte were evaluated by related gene expression and lipid staining. The expression of Keratin-1, 6, 17 protein was detected by western immunoblotting. The results showed that the above cytokines could be induced by latanoprost in meibomian gland epithelial cells. LG100268 and rosiglitazone could inhibit the production of IL-6 and TNF-α induced by latanoprost, respectively. Latanoprost suppressed the expression of differentiation-related mRNA through a positive feedback loop by enhancement of COX-2 expression via FP receptor-activated ERK signaling. The expression of Keratin-17 was upregulated by rosiglitazone and suppressed by LG100268. The application of IL-6 and TNF-α showed negative effects on lipid accumulation in meibomian gland epithelial cells. These results demonstrated that latanoprost could induce inflammation and suppress differentiation of mouse meibomian gland epithelial cells. The activation of PPAR-γ and RXR-α showed an anti-inflammatory effect, showing a potential role to antagonize the effect of latanoprost eyedrops on meibomian gland epithelial cells.

Metabolite G-Protein Coupled Receptors in Cardio-Metabolic Diseases

G protein-coupled receptors (GPCRs) have originally been described as a family of receptors activated by hormones, neurotransmitters, and other mediators. However, in recent years GPCRs have shown to bind endogenous metabolites, which serve functions other than as signaling mediators. These receptors respond to fatty acids, mono- and disaccharides, amino acids, or various intermediates and products of metabolism, including ketone bodies, lactate, succinate, or bile acids. Given that many of these metabolic processes are dysregulated under pathological conditions, including diabetes, dyslipidemia, and obesity, receptors of endogenous metabolites have also been recognized as potential drug targets to prevent and/or treat metabolic and cardiovascular diseases. This review describes G protein-coupled receptors activated by endogenous metabolites and summarizes their physiological, pathophysiological, and potential pharmacological roles.

Involvement of prostacyclin synthase in high-fat-diet-induced obesity

Prostacyclin (PGI2) synthase (PGIS) functions downstream of inducible cyclooxygenase COX-2 in the PGI2 biosynthetic pathway. Although COX-2 and PGI2 receptor (IP) are known to be involved in adipogenesis and obesity, the involvement of PGIS has not been fully elucidated. In this study, we examined the role of PGIS in adiposity by using PGIS-deficient mice. Although PGIS deficiency did not affect in vitro adipocyte differentiation, when fed a high-fat diet (HFD), PGIS knockout (KO) mice showed reductions in both body weight gain and epididymal fat mass relative to wild-type (WT) mice. PGIS deficiency might reduce HFD-induced obesity by suppressing PGI2 production. We further found that additional gene deletion of microsomal prostaglandin (PG) E synthase-1 (mPGES-1), one of the other PG terminal synthases that also functions downstream of COX-2, emphasized the metabolic phenotypes of PGIS-deficient mice. More marked reduction in obesity and improved insulin resistance were observed in PGIS/mPGES-1 double KO (DKO) mice. Since an additive increase in PGF2α level in epididymal fat was observed in DKO mice, mPGES-1 deficiency might affect adiposity by enhancing the production of PGF2α. Our immunohistochemical analysis further revealed that in adipose tissues, PGIS was expressed in vascular and stromal cells but not in adipocytes. These results suggested that PGI2 produced from PGIS-expressed stromal tissues might enhance HFD-induced obesity by acting on IP expressed in adipocytes. The balance of expressions of PG terminal synthases and the subsequent production of prostanoids might be critical for adiposity.

Gene Deletion of Calcium-Independent Phospholipase A2γ (iPLA2γ) Suppresses Adipogenic Differentiation of Mouse Embryonic Fibroblasts

Adipogenic differentiation is a complex process by which fibroblast-like undifferentiated cells are converted into cells that accumulate lipid droplets. We here investigated the effect of gene deletion of calcium-independent phospholipase A₂γ (iPLA₂γ), a membrane-bound PLA₂ enzyme, on adipogenic differentiation in mice. Since iPLA₂γ knockout (KO) mice showed reduced fat volume and weight, we prepared mouse embryonic fibroblasts (MEF) from wild-type (WT) and iPLA₂γ KO mice and examined the effect of iPLA₂γ deletion on in vitro adipogenic differentiation. iPLA₂γ increased during adipogenic differentiation in WT mouse-derived MEFs, and the differentiation was partially abolished in iPLA₂γ KO-derived MEFs. In KO-derived MEFs, the inductions of peroxisome proliferator activator receptor γ (PPARγ) and CAAT/enhancer-binding protein α (C/EBPα) were also reduced during adipogenic differentiation, and the reductions in PPARγ and C/EBPα expressions and the defect in adipogenesis were restored by treatment with troglitazone, a PPARγ ligand. These results indicate that iPLA₂γ might play a critical role in adipogenic differentiation by regulating PPARγ expression.

The Expression and Clinical Significance of Aldo-Keto Reductase 1 Member B1 in Gastric Carcinoma

To study the expression of aldo-keto reductase 1 member B1 (AKR1B1) in gastric carcinoma (GC), the correlation between AKR1B1 and the clinicopathological characteristics of GC patients, and provide reference for the diagnosis and prognosis of GC patients. One hundred thirty-six patients with GC were collected, and the expression level of AKR1B1 in GC and adjacent tissues was detected by immunohistochemistry assays. The clinicopathological features and prognosis of GC patients were collected to analyze the relationship with AKR1B1 expression. The positive expression of AKR1B1 in GC tissues was significantly higher than that of adjacent nontumor tissues. The difference of AKR1B1 expression between GC tissues and paired adjacent nontumor tissues was statistically significant (p < 0.001). AKR1B1 was closely related to tumor size, regional lymph node (N), metastases (M), and tumor-node-metastasis (TNM) stage (p < 0.05). The overall survival of patients with low expression of AKR1B1 was significantly better than that of patients with high expression of AKR1B1 by Kaplan-Meier survival analysis (p < 0.001). AKR1B1 plays an important role in the occurrence and development of GC, and it has a certain reference value for the prognosis of GC patients.

L-PGDS-produced PGD2 in premature, but not in mature, adipocytes increases obesity and insulin resistance

Lipocalin-type prostaglandin (PG) D synthase (L-PGDS) is responsible for the production of PGD₂ in adipocytes and is selectively induced by a high-fat diet (HFD) in adipose tissue. In this study, we investigated the effects of HFD on obesity and insulin resistance in two distinct types of adipose-specific L-PGDS gene knockout (KO) mice: fatty acid binding protein 4 (fabp4, aP2)-Cre/L-PGDS^flox/flox and adiponectin (AdipoQ)-Cre/L-PGDS^flox/flox mice. The L-PGDS gene was deleted in adipocytes in the premature stage of the former strain and after maturation of the latter strain. The L-PGDS expression and PGD₂ production levels decreased in white adipose tissue (WAT) under HFD conditions only in the aP2-Cre/L-PGDS^flox/flox mice, but were unchanged in the AdipoQ-Cre/L-PGDS^flox/flox mice. When fed an HFD, aP2-Cre/L-PGDS^flox/flox mice significantly reduced body weight gain, adipocyte size, and serum cholesterol and triglyceride levels. In WAT of the HFD-fed aP2-Cre/L-PGDS^flox/flox mice, the expression levels of the adipogenic, lipogenic, and M1 macrophage marker genes were decreased, whereas those of the lipolytic and M2 macrophage marker genes were enhanced or unchanged. Insulin sensitivity was improved in the HFD-fed aP2-Cre/L-PGDS^flox/flox mice. These results indicate that PGD₂ produced by L-PGDS in premature adipocytes is involved in the regulation of body weight gain and insulin resistance under nutrient-dense conditions.

Prostacyclin: A major prostaglandin in the regulation of adipose tissue development

Prostaglandins (PGs) belong to the group lipid mediators and can act as local hormones. They contain 20 carbon atoms, including a 5-carbon ring, and are biosynthesized from membrane phospholipid derived arachidonic acid through the arachidonate cyclooxygenase (COX) pathway with the help of various terminal synthase enzymes. Prostacyclin (prostaglandin I₂ ) is one of the major prostanoids produced with the help of prostacyclin synthase (prostaglandin I₂ synthase) enzyme and rapidly hydrolyzed into 6-keto-PGF_1α in biological fluids. Obesity indicates an excess of body adiposity, which is globally considered as one of the major health disasters responsible for developing complex pathological situations in the human body. Adipose tissues can produce various PGs, and thus, the level and the molecular activity of these endogenously synthesized PGs are considered critical for the development of obesity. In this regard, the involvement of prostacyclin in adipogenesis has been studied in the last few decades. The current review, along with the background of other related PGs, presents the several molecular aspects of endogenous prostaglandin I₂ in adipose tissue development. Especially, the regulation of life cycle of adipocytes, impact on terminal differentiation, activity through prostacyclin receptor (IP), autocrine-paracrine manner, thermogenic adipose tissue remodeling and some future experimental aspects of prostacyclin have been focused upon in this study. This discussion might assist to develop new drug molecules acting on the signaling pathways of prostacyclin and devise therapeutic strategies for treating obesity.

Kinetic effect of oestrogen on secretion of prostaglandins E2 and F2α in bovine oviduct epithelial cells

This study aimed to investigate the effect of oestrogen on prostaglandin E2 (PGE₂) and prostaglandin F2α (PGF_2α) secretion in bovine oviduct epithelial cells. Bovine oviduct epithelial cells were obtained from the lumen of fresh bovine oviducts. Quantitative real-time polymerase chain reaction and in-cell western assays were used to measure PGE₂ and PGF_2α synthase activity and enzyme-linked immunosorbent assays were used to detect the concentrations of the two prostaglandins in extracellular fluid. We observed that oestradiol caused a short-term increase in cyclo-oxygenase-2 (COX-2), which stimulated PGE₂ and PGF_2α secretion, and that a subsequent decrease in COX-2 and an increase in cyclo-oxygenase-1 (COX-1) produced a high PGE₂:PGF_2α ratio. These findings reflect the dynamic change in PGE₂ and PGF_2α levels under the influence of oestrogen, which may be essential for fertilisation.

Transcriptome Landscape of Porcine Intramuscular Adipocytes during Differentiation

The adipocyte differentiation process, controlled by a tightly regulated transcriptional cascade, contributes partly to determine intramuscular adipose tissue (IMAT) mass, which is associated with meat quality in food animals, as well as obesity and related metabolic complications in human. Thus, this study aimed to characterize genes critical for intramuscular preadipocyte differentiation. Primary intramuscular preadipocytes were isolated from pigs, and mRNA profiles were performed at several key points (0 h, 4 h, 8 h, 1 day, 2 days, and 6 days) during adipogenesis using microarrays. By gene functional analysis, we identified numerous differentially expressed genes among distinct stages of intramuscular preadipocyte differentiation, which included numbers of transcription factors in the early stages. We obtained 4 clusters of differential gene expression pattern, including crucial candidate genes associated with adipogenesis of intramuscular adipocytes. Further, we demonstrated that POSTN and FGFR4 suppressed, whereas AKR1CL1 promoted, the expression of adipogenic marker PPARγ and C/EBPα. Taken together, our data delineated the transcriptome landscape during porcine intramuscular preadipocyte differentiation, which provided a valuable resource for finding the genes responsible for IMAT formation.

Characterization of AKR1B16, a novel mouse aldo-keto reductase

Aldo-keto reductases (AKRs) are distributed in three families and multiple subfamilies in mammals. The mouse Akr1b3 gene is clearly orthologous to human AKR1B1, both coding for aldose reductase, and their gene products show similar tissue distribution, regulation by osmotic stress and kinetic properties. In contrast, no unambiguous orthologs of human AKR1B10 and AKR1B15.1 have been identified in rodents. Although two more AKRs, AKR1B7 and AKR1B8, have been identified and characterized in mouse, none of them seems to exhibit properties similar to the human AKRs. Recently, a novel mouse AKR gene, Akr1b16, was annotated and the respective gene product, AKR1B16 (sharing 83% and 80% amino acid sequence identity with AKR1B10 and AKR1B15.1, respectively), was expressed as insoluble and inactive protein in a bacterial expression system. Here we describe the expression and purification of a soluble and enzymatically active AKR1B16 from E. coli using three chaperone systems. A structural model of AKR1B16 allowed the estimation of its active-site pocket volume, which was much wider (402 Å³) than those of AKR1B10 (279 Å³) and AKR1B15.1 (60 Å³). AKR1B16 reduced aliphatic and aromatic carbonyl compounds, using NADPH as a cofactor, with moderate or low activity (highest k_cat values around 5 min^-1). The best substrate for the enzyme was pyridine-3-aldehyde. AKR1B16 showed poor inhibition with classical AKR inhibitors, tolrestat being the most potent. Kinetics and inhibition properties resemble those of rat AKR1B17 but differ from those of the human enzymes. In addition, AKR1B16 catalyzed the oxidation of 17β-hydroxysteroids in a NADP⁺-dependent manner. These results, together with a phylogenetic analysis, suggest that mouse AKR1B16 is an ortholog of rat AKR1B17, but not of human AKR1B10 or AKR1B15.1. These human enzymes have no counterpart in the murine species, which is evidenced by forming a separate cluster in the phylogenetic tree and by their unique activity with retinaldehyde.

Control of adipogenesis by oxylipins, GPCRs and PPARs

Oxylipins are bioactive metabolites derived from the oxygenation of ω3 and ω6 polyunsaturated fatty acids, triggered essentially by cyclooxygenase and lipoxygenase activities. Oxylipins are involved in the development and function of adipose tissue and their productions are strictly related to diet quality and quantity. Oxylipins signal via cell surface membrane (G Protein-coupled receptors) and nuclear receptors (peroxisome proliferator-activated receptors), two pathways playing a pivotal role in adipocyte biology. In this review, we made an attempt to cover the available knowledge about synthesis and molecular function of oxylipins known to modulate adipogenesis, adipocyte function and phenotype conversion, with a focus on their interaction with peroxisome proliferator-activated nuclear receptor family.

Tumorigenic potential is restored during differentiation in fusion-reprogrammed cancer cells

Detailed understanding of the mechanistic steps underlying tumor initiation and malignant progression is critical for insights of potentially novel therapeutic modalities. Cellular reprogramming is an approach of particular interest because it can provide a means to reset the differentiation state of the cancer cells and to revert these cells to a state of non-malignancy. Here, we investigated the relationship between cellular differentiation and malignant progression by the fusion of four independent mouse cancer cell lines from different tissues, each with differing developmental potentials, to pluripotent mouse embryonic stem (ES) cells. Fusion was accompanied by loss of differentiated properties of the four parental cancer cell lines and concomitant emergence of pluripotency, demonstrating the feasibility to reprogram the malignant and differentiative properties of cancer cells. However, the original malignant and differentiative phenotypes re-emerge upon withdrawal of the fused cells from the embryonic environment in which they were maintained. cDNA array analysis of the malignant hepatoma progression implicated a role for Foxa1, and silencing Foxa1 prevented the re-emergence of malignant and differentiation-associated gene expression. Our findings support the hypothesis that tumor progression results from deregulation of stem cells, and our approach provides a strategy to analyze possible mechanisms in the cancer initiation.

The effects of vascular endothelial growth factor (VEGF) on human orbital preadipocyte

PURPOSE

To investigate the presence of the Vascular Endothelial Growth Factor (VEGF) and its receptor (VEGFR) in human orbital preadipocytes, and to evaluate the effect of VEGF on human orbital preadipocyte differentiation and adipogenesis in vitro.

RESULTS

Four isoforms of VEGF (VEGF121, 155, 189, and 206), VEGFR-1, VEGF-2, and neuropilin-1 were expressed in human orbital preadipocytes. Treatment with 100 ng/ml VEGF induced higher expressions of C/EBPα and LPL than the non-treated control (p = 0.03 and p = 0.01) or treatment with 50ng/ml (p = 0.04 for both). At both concentrations VEGF enhanced the accumulation of intra-cytoplasmic lipid versus the control, and treatment with 100 ng/ml VEGF induced more lipid accumulation than treatment with 50 ng/ml VEGF (p = 0.03).

CONCLUSIONS

VEGF and VEGFR were observed in human orbital preadipocytes, and exogenous VEGF enhanced adipogenesis in these cells. These results suggest that VEGF plays a role as an autocrine or paracrine growth factor during human orbital preadipocyte differentiation.

Aldose reductases influence prostaglandin F2α levels and adipocyte differentiation in male mouse and human species

Aldose reductases (AKR1B) are widely expressed oxidoreductases whose physiological function remains elusive. Some isoforms are genuine prostaglandin F2α (PGF2α) synthases, suggesting they might influence adipose homeostasis because PGF2α inhibits adipogenesis. This was shown by Akr1b7 gene ablation in the mouse, which resulted in increased adiposity related to a lower PGF2α content in fat. Yet humans have no ortholog gene for Akr1b7, so the role of aldose reductases in human adipose homeostasis remains to be explored. We analyzed expression of genes encoding human and mouse aldose reductase isoforms in adipose tissues and differentiating adipocytes to assess conserved mechanisms regulating PGF2α synthesis and adipogenesis. The Akr1b3 gene encoded the most abundant isoform in mouse adipose tissue, whereas Akr1b7 encoded the only isoform enriched in the stromal vascular fraction. Most mouse aldose reductase gene expression peaked in early adipogenesis of 3T3-L1 cells and diminished with differentiation. In contrast with its mouse ortholog Akr1b3, AKR1B1 expression increased throughout differentiation of human multipotent adipose-derived stem cells, paralleling PGF2α release, whereas PGF2α receptor (FP) levels collapsed in early differentiation. Pharmacological inhibition of aldose reductase using Statil altered PGF2α production and enhanced human multipotent adipose-derived stem adipocyte differentiation. As expected, the adipogenic effects of Statil were counteracted by an FP agonist (cloprostenol). Thus, in both species aldose reductase-dependent PGF2α production could be important in early differentiation to restrict adipogenesis. PGF2α antiadipogenic signaling could then be toned down through the FP receptor or aldose reductases down-regulation in human and mouse cells, respectively. Our data suggest that aldose reductase inhibitors could have obesogenic potential.

Expression of genes related to prostaglandin synthesis or signaling in human subcutaneous and omental adipose tissue: depot differences and modulation by adipogenesis

OBJECTIVES

(1) To examine depot-specific PGE2 and PGF2α release and mRNA expression of enzymes or receptors involved in PG synthesis or signaling in human adipose tissues; (2) to identify changes in expression of these transcripts through preadipocyte differentiation; and (3) to examine associations between adipose tissue mRNA expression of these transcripts and adiposity measurements.

METHODS

Fat samples were obtained surgically in women. PGE2 and PGF2α release by preadipocytes and adipose tissue explants was measured. Expression levels of mRNA coding for enzymes or receptors involved in PG synthesis or signaling were measured by RT-PCR.

RESULTS

Cultured preadipocytes and explants from omental fat released more PGE2 and PGF2α than those from the subcutaneous depot and the corresponding transcripts showed consistent depot differences. Following preadipocyte differentiation, expression of PLA2G16 and PTGER3 mRNA was significantly increased whereas COX-1, COX-2, PTGIS, and PTGES mRNA abundance were decreased in both compartments (P ≤ 0.01 for all). Transcripts that were stimulated during adipogenesis were those that correlated best with adiposity measurements.

CONCLUSION

Cells from the omental fat compartment release more PGE2 and PGF2α than those from the subcutaneous depot. Obesity modulates expression of PG-synthesizing enzymes and PG receptors which likely occurs through adipogenesis-induced changes in expression of these transcripts.

Lipid signaling in adipose tissue: Connecting inflammation & metabolism

Obesity-associated low-grade inflammation of white adipose tissue (WAT) contributes to development of insulin resistance and other disorders. Accumulation of immune cells, especially macrophages, and macrophage polarization from M2 to M1 state, affect intrinsic WAT signaling, namely anti-inflammatory and proinflammatory cytokines, fatty acids (FA), and lipid mediators derived from both n-6 and n-3 long-chain PUFA such as (i) arachidonic acid (AA)-derived eicosanoids and endocannabinoids, and (ii) specialized pro-resolving lipid mediators including resolvins derived from both eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), lipoxins (AA metabolites), protectins and maresins (DHA metabolites). In this respect, potential differences in modulating adipocyte metabolism by various lipid mediators formed by inflammatory M1 macrophages typical of obese state, and non-inflammatory M2 macrophages typical of lean state remain to be established. Studies in mice suggest that (i) transient accumulation of M2 macrophages could be essential for the control of tissue FA levels during activation of lipolysis, (ii) currently unidentified M2 macrophage-borne signaling molecule(s) could inhibit lipolysis and re-esterification of lipolyzed FA back to triacylglycerols (TAG/FA cycle), and (iii) the egress of M2 macrophages from rebuilt WAT and removal of the negative feedback regulation could allow for a full unmasking of metabolic activities of adipocytes. Thus, M2 macrophages could support remodeling of WAT to a tissue containing metabolically flexible adipocytes endowed with a high capacity of both TAG/FA cycling and oxidative phosphorylation. This situation could be exemplified by a combined intervention using mild calorie restriction and dietary supplementation with EPA/DHA, which enhances the formation of "healthy" adipocytes. This article is part of a Special Issue entitled Oxygenated metabolism of PUFA: analysis and biological relevance."

The ω6-fatty acid, arachidonic acid, regulates the conversion of white to brite adipocyte through a prostaglandin/calcium mediated pathway

Objective

Brite adipocytes are inducible energy-dissipating cells expressing UCP1 which appear within white adipose tissue of healthy adult individuals. Recruitment of these cells represents a potential strategy to fight obesity and associated diseases.

Methods/Results

Using human Multipotent Adipose-Derived Stem cells, able to convert into brite adipocytes, we show that arachidonic acid strongly inhibits brite adipocyte formation via a cyclooxygenase pathway leading to secretion of PGE2 and PGF2α. Both prostaglandins induce an oscillatory Ca⁺⁺ signaling coupled to ERK pathway and trigger a decrease in UCP1 expression and in oxygen consumption without altering mitochondriogenesis. In mice fed a standard diet supplemented with ω6 arachidonic acid, PGF2α and PGE2 amounts are increased in subcutaneous white adipose tissue and associated with a decrease in the recruitment of brite adipocytes.

Conclusion

Our results suggest that dietary excess of ω6 polyunsaturated fatty acids present in Western diets, may also favor obesity by preventing the “browning” process to take place.

Suppression of adipogenesis by valproic acid through repression of USF1-activated fatty acid synthesis in adipocytes

Valproic acid suppresses the accumulation of the intracellular lipids through suppression of fatty acid synthesis via repression of USF1-mediated expression of the fatty acid synthase gene in adipocytes.

Termination mechanism of CREB-dependent activation of COX-2 expression in early phase of adipogenesis

We elucidated the molecular mechanism of prostaglandin (PG) E2- and PGF2α-mediated suppression of the early phase of adipogenesis through enhanced COX-2 expression in 3T3-L1 cells. 3-Isobutyl-1-methylxanthine, an inhibitor of phosphodiesterase which catalyzes the conversion of cAMP to AMP, enhanced the activity of protein kinase A (PKA). Dibutyryl cAMP activated PKA and enhanced the phosphorylation of cAMP response element (CRE)-binding protein (CREB). The ability of CREB binding to the CRE of the COX-2 promoter was elevated for enhancement of the expression of the COX-2 gene. CREB siRNA suppressed the expression of the COX-2 gene. Furthermore, okadaic acid, a protein phosphatase (PP) 1/2A inhibitor, suppressed the progression of adipogenesis by preventing PP1/2A-mediated suppression of CREB-dependent COX-2 expression, thus resulting in increased production of anti-adipogenic PGE2 and PGF2α. These results indicate that CREB-dependent expression of COX-2 for the production of anti-adipogenic PGs is critical for the regulation of the early phase of adipogenesis.

Prostaglandin (PG) F2 alpha synthesis in human subcutaneous and omental adipose tissue: modulation by inflammatory cytokines and role of the human aldose reductase AKR1B1

INTRODUCTION

PGF2α may be involved in the regulation of adipose tissue function.

OBJECTIVES

1) To examine PGF2α release by primary preadipocytes, mature adipocytes and whole tissue explants from the subcutaneous and omental fat compartments; 2) To assess which PGF synthase is the most relevant in human adipose tissue.

METHODS

Fat samples were obtained by surgery in women. PGF2α release by preadipocytes, adipocytes and explants under stimulation by TNF-α, IL-1β or both was measured. Messenger RNA expression levels of AKR1B1 and AKR1C3 were measured by RT-PCR in whole adipose tissue and cytokine-treated preadipocytes. The effect of AKR1B1 inhibitor ponalrestat on PGF2α synthesis was investigated.

RESULTS

PGF2α release was significantly induced in response to cytokines compared to control in omental (p = 0.01) and to a lesser extent in subcutaneous preadipocytes (p = 0.02). Messenger RNA of COX-2 was significantly higher in omental compared to subcutaneous preadipocytes in response to combined TNF-α and IL-1β (p = 0.01). Inflammatory cytokines increased AKR1B1 mRNA expression and protein levels (p≤0.05), but failed to increase expression levels of AKR1C3 in cultured preadipocytes. Accordingly, ponalrestat blunted PGF2α synthesis by preadipocytes in basal and stimulated conditions (p≤0.05). Women with the highest PGF2α release by omental adipocytes had a higher BMI (p = 0.05), waist circumference (p≤0.05) and HOMAir index (p≤0.005) as well as higher mRNA expression of AKR1B1 in omental (p<0.10) and subcutaneous (p≤0.05) adipose tissue compared to women with low omental adipocytes PGF2α release. Positive correlations were observed between mRNA expression of AKR1B1 in both compartments and BMI, waist circumference as well as HOMAir index (p≤0.05 for all).

CONCLUSION

PGF2α release by omental mature adipocytes is increased in abdominally obese women. Moreover, COX-2 expression and PGF2α release is particularly responsive to inflammatory stimulation in omental preadipocytes. Yet, blockade of PGF synthase AKR1B1 inhibits most of the PGF2α release.

Activation of early phase of adipogenesis through Krüppel-like factor KLF9-mediated, enhanced expression of CCAAT/enhancer-binding protein β in 3T3-L1 cells

In this study, we found that Krüppel-like factor (KLF) 9 activate the progression of the early phase of adipocyte differentiation in mouse adipocytic 3T3-L1 cells. KLF9 mRNA was detected in preadipocytes; and its level increased after the initiation of adipocyte differentiation, reached its maximum at 1h, and gradually decreased thereafter. Functional suppression of KLF9 mRNA by its siRNAs repressed the accumulation of the intracellular lipids with a reduction in the expression of CCAAT/enhancer-binding protein (C/EBP) β, but not in that of C/EBPδ. In contrast, C/EBPβ and C/EBPδ did not affect the expression of KLF9 in 3T3-L1 cells. A chromatin immunoprecipitation assay revealed that KLF9 bound the KLF binding element at position -874 of the mouse C/EBPβ promoter. Moreover, the ability of KLF9 to bind to this element was enhanced, with a peak at 1-2h after the initiation of adipogenesis, whose profile well resembled that of the expression of the C/EBPβ gene in 3T3-L1 cells. These results indicate that KLF9 activated the early phase of adipogenesis by enhancing the expression of the C/EBPβ gene in 3T3-L1 cells.

Prostaglandin reductase-3 negatively modulates adipogenesis through regulation of PPARγ activity

Adipocyte differentiation is a multistep program under regulation by several factors. Peroxisome proliferator-activated receptor γ (PPARγ) serves as a master regulator of adipogenesis. However, the endogenous ligand for PPARγ remained elusive until 15-keto-PGE2 was identified recently as an endogenous PPARγ ligand. In this study, we demonstrate that zinc-containing alcohol dehydrogenase 2 (ZADH2; here termed prostaglandin reductase-3, PTGR-3) is a new member of prostaglandin reductase family that converts 15-keto-PGE2 to 13,14-dihydro-15-keto-PGE2. Adipogenesis is accelerated when endogenous PTGR-3 is silenced in 3T3-L1 preadipocytes, whereas forced expression of PTGR-3 significantly decreases adipogenesis. PTGR-3 expression decreased during adipocyte differentiation, accompanied by an increased level of 15-keto-PGE2. 15-keto-PGE2 exerts a potent proadipogenic effect by enhancing PPARγ activity, whereas overexpression of PTGR-3 in 3T3-L1 preadipocytes markedly suppressed the proadipogenic effect of 15-keto-PGE2 by repressing PPARγ activity. Taken together, these findings demonstrate for the first time that PTGR-3 is a novel 15-oxoprostaglandin-Δ(13)-reductase and plays a critical role in modulation of normal adipocyte differentiation via regulation of PPARγ activity. Thus, modulation of PTGR-3 might provide a novel avenue for treating obesity and related metabolic disorders.

Anandamide-derived prostamide F2α negatively regulates adipogenesis

Lipid mediators variedly affect adipocyte differentiation. Anandamide stimulates adipogenesis via CB1 receptors and peroxisome proliferator-activated receptor γ. Anandamide may be converted by PTGS2 (COX2) and prostaglandin F synthases, such as prostamide/prostaglandin F synthase, to prostaglandin F2α ethanolamide (PGF2αEA), of which bimatoprost is a potent synthetic analog. PGF2αEA/bimatoprost act via prostaglandin F2αFP receptor/FP alt4 splicing variant heterodimers. We investigated whether prostamide signaling occurs in preadipocytes and controls adipogenesis. Exposure of mouse 3T3-L1 or human preadipocytes to PGF2αEA/bimatoprost during early differentiation inhibits adipogenesis. PGF2αEA is produced from anandamide in preadipocytes and much less so in differentiating adipocytes, which express much less PTGS2, FP, and its alt4 splicing variant. Selective antagonism of PGF2αEA receptors counteracts prostamide effects on adipogenesis, as does inhibition of ERK1/2 phosphorylation. Selective inhibition of PGF2αEA versus prostaglandin F2α biosynthesis accelerates adipogenesis. PGF2αEA levels are reduced in the white adipose tissue of high fat diet-fed mice where there is a high requirement for new adipocytes. Prostamides also inhibit zebrafish larval adipogenesis in vivo. We propose that prostamide signaling in preadipocytes is a novel anandamide-derived antiadipogenic mechanism.

A new approach to detect small peptides clearly and sensitively by Western blotting using a vacuum-assisted detection method

Western blotting is a widely used technique for the detection and quantification of proteins and peptides. However, it is challenging to detect small peptides efficiently by the conventional Western blotting method with shaking, in part because the peptides readily detach from the blotted membrane. Although some modified Western blotting protocols have been developed to overcome this problem, it remains difficult to prevent peptide detachment from the membrane. In this study, we show that the previously developed vacuum-assisted detection method greatly improves the detection of small peptides without additional protocol modification. The vacuum-assisted method was developed to shorten the time required for all immunodetection steps, and all the Western blotting solutions penetrated the membrane quickly and efficiently by this method. By using this vacuum method, we succeeded in detecting small peptides that were completely undetectable by the conventional Western blotting method. We also confirmed that peptide detachment was induced even by gentle shaking in the case of the conventional method, and the detachment was accelerated when detergent was present in the buffer. Unlike in the conventional method, there is no need to shake the membrane in solution in the vacuum method. Therefore, it is thought that the small peptides could be detected sensitively only by the vacuum method.

Butein is a novel anti-adipogenic compound

Rhus verniciflua Stokes (RVS) has been used as a traditional herbal medicine for its various biological activities including anti-adipogenic effects. Activity-guided separation led to the identification of the anti-adipogenic functions of butein. Butein, a novel anti-adipogenic compound, robustly suppressed lipid accumulation and inhibited expression of adipogenic markers. Molecular studies showed that activated transforming growth factor-β (TGF-β) and suppressed signal transducer and activator of transcription 3 (STAT3) signaling pathways were mediated by butein. Analysis of the temporal expression profiles suggests that TGF-β signaling precedes the STAT3 in the butein-mediated anti-adipogenic cascade. Small interfering RNA-mediated silencing of STAT3 or SMAD2/3 blunted the inhibitory effects of butein on adipogenesis indicating that an interaction between two signaling pathways is required for the action of butein. Upon butein treatments, stimulation of TGF-β signaling was still preserved in STAT3 silenced cells, whereas regulation of STAT3 signaling by butein was significantly impaired in SMAD2/3 silenced cells, further showing that TGF-β acts upstream of STAT3 in the butein-mediated anti-adipogenesis. Taken together, the present study shows that butein, a novel anti-adipogenic compound from RVS, inhibits adipocyte differentiation through the TGF-β pathway followed by STAT3 and peroxisome proliferator-activated receptor γ signaling, further implicating potential roles of butein in TGF-β- and STAT3-dysregulated diseases.

Prostaglandins as PPARγ Modulators in Adipogenesis

Adipocytes and fat cells play critical roles in the regulation of energy homeostasis. Adipogenesis (adipocyte differentiation) is regulated via a complex process including coordinated changes in hormone sensitivity and gene expression. PPARγ is a ligand-dependent transcription factor and important in adipogenesis, as it enhances the expression of numerous adipogenic and lipogenic genes in adipocytes. Prostaglandins (PGs), which are lipid mediators, are associated with the regulation of PPARγ function in adipocytes. Prostacyclin promotes the differentiation of adipocyte-precursor cells to adipose cells via activation of the expression of C/EBPβ and δ. These proteins are important transcription factors in the activation of the early phase of adipogenesis, and they activate the expression of PPARγ, which event precedes the maturation of adipocytes. PGE₂ and PGF_2α strongly suppress the early phase of adipocyte differentiation by enhancing their own production via receptor-mediated elevation of the expression of cycloxygenase-2, and they also suppress the function of PPARγ. In contrast, PGD₂ and its non-enzymatic metabolite, Δ¹²-PGJ₂, activate the middle-late phase of adipocyte differentiation through both DP2 receptors and PPARγ. This paper focuses on potential roles of PGs as PPARγ modulators in adipogenesis and regulators of obesity.

Depressed levels of prostaglandin F2α in mice lacking Akr1b7 increase basal adiposity and predispose to diet-induced obesity

Negative regulators of white adipose tissue (WAT) expansion are poorly documented in vivo. Prostaglandin F(2α) (PGF(2α)) is a potent antiadipogenic factor in cultured preadipocytes, but evidence for its involvement in physiological context is lacking. We previously reported that Akr1b7, an aldo-keto reductase enriched in adipose stromal vascular fraction but absent from mature adipocytes, has antiadipogenic properties possibly supported by PGF(2α) synthase activity. To test whether lack of Akr1b7 could influence WAT homeostasis in vivo, we generated Akr1b7(-/-) mice in 129/Sv background. Akr1b7(-/-) mice displayed excessive basal adiposity resulting from adipocyte hyperplasia/hypertrophy and exhibited greater sensitivity to diet-induced obesity. Following adipose enlargement and irrespective of the diet, they developed liver steatosis and progressive insulin resistance. Akr1b7 loss was associated with decreased PGF(2α) WAT contents. Cloprostenol (PGF(2α) agonist) administration to Akr1b7(-/-) mice normalized WAT expansion by affecting both de novo adipocyte differentiation and size. Treatment of 3T3-L1 adipocytes and Akr1b7(-/-) mice with cloprostenol suggested that decreased adipocyte size resulted from inhibition of lipogenic gene expression. Hence, Akr1b7 is a major regulator of WAT development through at least two PGF(2α)-dependent mechanisms: inhibition of adipogenesis and lipogenesis. These findings provide molecular rationale to explore the status of aldo-keto reductases in dysregulations of adipose tissue homeostasis.

Synergistic suppression of early phase of adipogenesis by microsomal PGE synthase-1 (PTGES1)-produced PGE2 and aldo-keto reductase 1B3-produced PGF2α

We recently reported that aldo-keto reductase 1B3-produced prostaglandin (PG) F_2α suppressed the early phase of adipogenesis. PGE₂ is also known to suppress adipogenesis. In this study, we found that microsomal PGE₂ synthase (PGES)-1 (mPGES-1; PTGES1) acted as the PGES in adipocytes and that PGE₂ and PGF_2α synergistically suppressed the early phase of adipogenesis. PGE₂ production was detected in preadipocytes and transiently enhanced at 3 h after the initiation of adipogenesis of mouse adipocytic 3T3-L1 cells, followed by a quick decrease; and its production profile was similar to the expression of the cyclooxygenase-2 (PTGS2) gene. When 3T3-L1 cells were transfected with siRNAs for any one of the three major PTGESs, i.e., PTGES1, PTGES2 (mPGES-2), and PTGES3 (cytosolic PGES), only PTGES1 siRNA suppressed PGE₂ production and enhanced the expression of adipogenic genes. AE1-329, a PTGER4 (EP4) receptor agonist, increased the expression of the Ptgs2 gene with a peak at 1 h after the initiation of adipogenesis. PGE₂-mediated enhancement of the PTGS2 expression was suppressed by the co-treatment with L-161982, a PTGER4 receptor antagonist. Moreover, AE1-329 enhanced the expression of the Ptgs2 gene by binding of the cyclic AMP response element (CRE)-binding protein to the CRE of the Ptgs2 promoter; and its binding was suppressed by co-treatment with L-161982, which was demonstrated by promoter luciferase and chromatin immunoprecipitation assays. Furthermore, when 3T3-L1 cells were caused to differentiate into adipocytes in medium containing both PGE₂ and PGF_2α, the expression of the adipogenic genes and the intracellular triglyceride level were decreased to a greater extent than in medium containing either of them, revealing that PGE₂ and PGF_2α independently suppressed adipogenesis. These results indicate that PGE₂ was synthesized by PTGES1 in adipocytes and synergistically suppressed the early phase of adipogenesis of 3T3-L1 cells in cooperation with PGF_2α through receptor-mediated activation of PTGS2 expression.

Aldo-Keto Reductases 1B in Endocrinology and Metabolism

The aldose reductase (AR; human AKR1B1/mouse Akr1b3) has been the focus of many research because of its role in diabetic complications. The starting point of these alterations is the massive entry of glucose in polyol pathway where it is converted into sorbitol by this enzyme. However, the issue of AR function in non-diabetic condition remains unresolved. AR-like enzymes (AKR1B10, Akr1b7, and Akr1b8) are highly related isoforms often co-expressed with bona fide AR, making functional analysis of one or the other isoform a challenging task. AKR1B/Akr1b members share at least 65% protein identity and the general ability to reduce many redundant substrates such as aldehydes provided from lipid peroxidation, steroids and their by-products, and xenobiotics in vitro. Based on these properties, AKR1B/Akr1b are generally considered as detoxifying enzymes. Considering that divergences should be more informative than similarities to help understanding their physiological functions, we chose to review specific hallmarks of each human/mouse isoforms by focusing on tissue distribution and specific mechanisms of gene regulation. Indeed, although the AR shows ubiquitous expression, AR-like proteins exhibit tissue-specific patterns of expression. We focused on three organs where certain isoforms are enriched, the adrenal gland, enterohepatic, and adipose tissues and tried to connect recent enzymatic and regulation data with endocrine and metabolic functions of these organs. We presented recent mouse models showing unsuspected physiological functions in the regulation of glucido-lipidic metabolism and adipose tissue homeostasis. Beyond the widely accepted idea that AKR1B/Akr1b are detoxification enzymes, these recent reports provide growing evidences that they are able to modify or generate signal molecules. This conceptually shifts this class of enzymes from unenviable status of scavenger to upper class of messengers.

Very long-chain-fatty acids enhance adipogenesis through coregulation of Elovl3 and PPARγ in 3T3-L1 cells

Here, we show that Elovl3 (elongation of very long-chain fatty acids 3) was involved in the regulation of the progression of adipogenesis through activation of peroxisome proliferator-activated receptor (PPAR)γ in mouse adipocytic 3T3-L1 cells. The expression of the Elovl3 gene increased during adipogenesis, the expression pattern of which was similar to that of the PPARγ gene. Troglitazone, a PPARγ agonist, enhanced Elovl3 expression in adipocytes, as it did that of other PPARγ target genes. Promoter-reporter analysis demonstrated that three PPAR-responsive elements in the Elovl3 gene promoter had the potential to activate its expression in 3T3-L1 cells. Moreover, a chromatin immunoprecipitation assay revealed that PPARγ bound these PPAR-responsive elements of the Elovl3 promoter. When the Elovl3 mRNA level was suppressed by its siRNAs, the level of intracellular triglycerides was significantly decreased, and the expression levels of adipogenic, lipolytic, and lipogenic genes were also repressed. In a mammalian two-hybrid assay, C18:1 and C20:1 very long-chain fatty acids (VLCFAs), which are the products of Elovl3 and activated PPARγ function. In addition, these same VLCFAs could prevent the Elovl3 siRNA-mediated suppression of adipogenesis by enhancing the expression of adipogenic, lipolytic, and lipogenic genes in adipocytes. Moreover, this VLCFAs-mediated activation was repressed by a PPARγ antagonist. These results indicate that the expression of the Elovl3 gene was activated by PPARγ during adipogenesis. Elovl3-produced C18:1 and C20:1 VLCFAs acted as agonists of PPARγ in 3T3-L1 cells. Thus, the Elovl3-PPARγ cascade is a novel regulatory circuit for the regulation of adipogenesis through improvement of PPARγ function in adipocytes.

Activation of adipogenesis by lipocalin-type prostaglandin D synthase-generated Δ¹²-PGJ₂ acting through PPARγ-dependent and independent pathways

Lipocalin-type prostaglandin (PG) D synthase (L-PGDS)-produced PGD(2) accelerates adipogenesis. In this study, we investigated the molecular mechanism of PGD(2)-mediated activation of adipogenesis in mouse adipocytic 3T3-L1 cells. LC/MS analysis showed that Δ(12)-PGJ(2), one of the PGD(2) metabolites, was predominantly produced in the differentiated 3T3-L1 cells. Δ(12)-PGJ(2) enhanced the expression of adipogenic genes in a Δ(12)-PGJ(2)-concentration-dependent manner. Suppression of the expression of the adipogenic genes by L-PGDS siRNA or AT-56, an L-PGDS inhibitor, was cleared by the addition of Δ(12)-PGJ(2). Moreover, the production of adiponectin and leptin was increased by treatment with Δ(12)-PGJ(2). Furthermore, the results of a mammalian two-hybrid assay demonstrated that Δ(12)-PGJ(2) enhanced the PPARγ-mediated transcription activity. However, Δ(12)-PGJ(2)-activated expression of adipogenic genes such as fatty acid binding protein 4 (aP2) and stearoyl-CoA desaturase was inhibited only at 38% and 42%, respectively, by treatment with GW9662, a PPARγ antagonist in 3T3-L1 cells, although Troglitazone-mediated activation of the expression of these adipogenic genes was completely suppressed by GW9662, suggesting the existence of a PPARγ-independent mechanism for Δ(12)-PGJ(2)-activated adipogenesis. These results, taken together, indicate that Δ(12)-PGJ(2) is a dominant metabolite of L-PGDS-produced PGD(2) during adipogenesis and acts as an activator for adipogenesis through both PPARγ-dependent and -independent mechanisms in 3T3-L1 cells.

Lipocalin-type prostaglandin D synthase protects against oxidative stress-induced neuronal cell death

L-PGDS [lipocalin-type PGD (prostaglandin D) synthase] is a dual-functional protein, acting as a PGD2-producing enzyme and a lipid transporter. L-PGDS is a member of the lipocalin superfamily and can bind a wide variety of lipophilic molecules. In the present study we demonstrate the protective effect of L-PGDS on H2O2-induced apoptosis in neuroblastoma cell line SH-SY5Y. L-PGDS expression was increased in H2O2-treated neuronal cells, and the L-PGDS level was highly associated with H2O2-induced apoptosis, indicating that L-PGDS protected the neuronal cells against H2O2-mediated cell death. A cell viability assay revealed that L-PGDS protected against H2O2-induced cell death in a concentration-dependent manner. Furthermore, the titration of free thiols in H2O2-treated L-PGDS revealed that H2O2 reacted with the thiol of Cys65 of L-PGDS. The MALDI-TOF (matrix-assisted laser-desorption ionization-time-of-flight)-MS spectrum of H2O2-treated L-PGDS showed a 32 Da increase in the mass relative to that of the untreated protein, showing that the thiol was oxidized to sulfinic acid. The binding affinities of oxidized L-PGDS for lipophilic molecules were comparable with those of untreated L-PGDS. Taken together, these results demonstrate that L-PGDS protected against neuronal cell death by scavenging reactive oxygen species without losing its ligand-binding function. The novel function of L-PGDS could be useful for the suppression of oxidative stress-mediated neurodegenerative diseases.

Antiadipogenic effect of dietary apigenin through activation of AMPK in 3T3-L1 cells

Adipocyte differentiation (adipogenesis) is a complex process including the coordinated changes in hormone sensitivity and gene expression in response to various stimuli. Natural compounds are known to be involved in the regulation of this process. Here we investigated the effects of dietary apigenin, a plant flavonoid, on adipogenesis. Apigenin suppressed adipocyte differentiation of mouse adipocytic 3T3-L1 cells and reduced the accumulation of intracellular lipids. Quantitative PCR and Western blot analyses revealed that apigenin decreased the levels of peroxisome proliferator-activated receptor γ and its target genes such as fatty acid binding protein 4 (aP2) and stearoyl-CoA desaturase. Apigenin decreased or had no effect on the expression of lipolytic genes such as adipose triglyceride lipase, hormone sensitive lipase, and monoacyl glyceride lipase, thereby reducing glycerol release from adipocytes. Noteworthily, apigenin activated 5'-adenosine monophosphate-activated protein kinase (AMPK) in an apigenin dose-dependent manner, which activation is known to suppress adipogenesis. These results provide a novel insight into the molecular mechanism involved in the action of apigenin: the apigenin-induced activation of AMPK leads to decreased expression of adipogenic and lipolytic genes, thus suppressing adipogenesis in 3T3-L1 cells. Thus, dietary apigenin may contribute to lower body-fat content and body-weight gain through the activation of AMPK.

In vitro study of antiadipogenic profile of latanoprost, travoprost, bimatoprost, and tafluprost in human orbital preadiopocytes

PURPOSE

To investigate the effect of prostaglandin F2α (PGF2α), latanoprost, travoprost, bimatoprost, and tafluprost on human orbital preadipocyte differentiation and intracellular lipid storage, and to reveal the potential mechanisms by which topical prostaglandin analogs induce orbital fat volume reduction and cause deep superior sulcus syndrome.

METHODS

Human orbital adipose precursors were treated in vitro for 24 h (day 1) with PGF2α, latanoprost, travoprost, bimatoprost, and tafluprost in their commercial formulations (1:100 dilution). Expressions of adipogenic transcription factor, peroxisome proliferator-activated receptor-gamma (PPARγ), and CCAAT-enhancer-binding protein α (C/EBPα) were determined by real-time reverse transcription-polymerase chain reaction (RT-PCR) at day 7. At 14 days, cells were stained with oil red O, intracellular lipid accumulation was evaluated by lipid absorbance, and adipocyte expression marker [Lipoprotein lipase (LPL)] was determined by real-time RT-PCR.

RESULTS

Our results showed that PGF2α and topical prostaglandin analogs down-regulated the expression of PPARγ and C/EBPα, and inhibited accumulation of intra-cytoplasmic lipid droplets and expression of LPL compared with the untreated control. Comparison between the 4 drugs showed that latanoprost had the weakest antiadipogenic effect, and bimatoprost induced the most significant reduction of adipogenesis.

CONCLUSION

Latanoprost, travoprost, bimatoprost, and tafluprost inhibited human preadipocyte differentiation and intracellular lipid accumulation. Morphologic and metabolic changes in orbital adipocytes caused by PGF2α analogs are a possible pathophysiologic explanation of superior eyelid deepening in patients with glaucoma.

Protective effects of quercetin against hydrogen peroxide-induced apoptosis in human neuronal SH-SY5Y cells

Hydrogen peroxide (H(2)O(2)) is a major reactive oxygen species that has been implicated in various neurodegenerative diseases. Quercetin, one of the plant flavonoids, has been reported to harbor various physiological properties including antioxidant activity. In this study, we investigated the neuroprotective effects of quercetin against H(2)O(2)-induced apoptosis in human neuronal SH-SY5Y cells. H(2)O(2)-mediated cytotoxicity and lactate dehydrogenase release were suppressed in a quercetin concentration-dependent manner. In addition, quercetin repressed the expression of the pro-apoptotic Bax gene and enhanced that of the anti-apoptotic Bcl-2 gene in SH-SY5Y cells. Moreover, quercetin effectively inhibited the activation of the caspase cascade that leads to DNA fragmentation, a key feature of apoptosis, and subsequent cell death. These results indicate the importance of quercetin in protecting against H(2)O(2)-mediated neuronal cell death. Thus, quercetin might potentially serve as an agent for prevention of neurodegenerative diseases caused by oxidative stress and apoptosis.

Hepatic xenobiotic metabolizing enzyme and transporter gene expression through the life stages of the mouse

BACKGROUND

Differences in responses to environmental chemicals and drugs between life stages are likely due in part to differences in the expression of xenobiotic metabolizing enzymes and transporters (XMETs). No comprehensive analysis of the mRNA expression of XMETs has been carried out through life stages in any species.

RESULTS

Using full-genome arrays, the mRNA expression of all XMETs and their regulatory proteins was examined during fetal (gestation day (GD) 19), neonatal (postnatal day (PND) 7), prepubescent (PND32), middle age (12 months), and old age (18 and 24 months) in the C57BL/6J (C57) mouse liver and compared to adults. Fetal and neonatal life stages exhibited dramatic differences in XMET mRNA expression compared to the relatively minor effects of old age. The total number of XMET probe sets that differed from adults was 636, 500, 84, 5, 43, and 102 for GD19, PND7, PND32, 12 months, 18 months and 24 months, respectively. At all life stages except PND32, under-expressed genes outnumbered over-expressed genes. The altered XMETs included those in all of the major metabolic and transport phases including introduction of reactive or polar groups (Phase I), conjugation (Phase II) and excretion (Phase III). In the fetus and neonate, parallel increases in expression were noted in the dioxin receptor, Nrf2 components and their regulated genes while nuclear receptors and regulated genes were generally down-regulated. Suppression of male-specific XMETs was observed at early (GD19, PND7) and to a lesser extent, later life stages (18 and 24 months). A number of female-specific XMETs exhibited a spike in expression centered at PND7.

CONCLUSIONS

The analysis revealed dramatic differences in the expression of the XMETs, especially in the fetus and neonate that are partially dependent on gender-dependent factors. XMET expression can be used to predict life stage-specific responses to environmental chemicals and drugs.