Coordinated Regulation of PPARγ Expression and Activity through Control of Chromatin Structure in Adipogenesis and Obesity

Profiling of m6A methylation in porcine intramuscular adipocytes and unravelling PHKG1 represses porcine intramuscular lipid deposition in an m6A-dependent manner

Intramuscular fat (IMF) content is mainly determined by intramuscular preadipocyte adipogenesis. Epigenetic modifications are known to have a regulatory effect on IMF. As N6-methyladenosine (m6A) is the most abundant epigenetic modification in eukaryotic RNAs. In the present study, we used m6A methylation and RNA sequencing (seq) to identify the m6A-modified RNAs associated with the adipogenic differentiation of intramuscular preadipocytes. Among them, the expression and m6A level of phosphorylase kinase subunit G1 (PHKG1) were found to be significantly changed during adipogenesis. Further studies revealed that knockdown of the methylase METTL3 decreased the m6A methylation of PHKG1 and led to a reduction in PHKG1. Moreover, knockdown of PHKG1 promoted adipogenic differentiation by upregulating the expression of adipogenic genes. In addition, we found that the IMF content in the longissimus thoracis (LT) of Bamei (BM) pigs was greater than that in Large White (LW) pigs, whereas the m6A and PHKG1 expression levels were lower in BM pigs. These findings indicate that the m6A level and expression of PHKG1 were significantly correlated with IMF content and meat quality. In conclusion, this study sheds light on the mechanism by which m6A modification regulates IMF deposition.

Exploring the Regulatory Role of ncRNA in NAFLD: A Particular Focus on PPARs

Liver diseases are responsible for global mortality and morbidity and are a significant cause of death worldwide. Consequently, the advancement of new liver disease targets is of great interest. Non-coding RNA (ncRNA), such as microRNA (miRNA) and long ncRNA (lncRNA), has been proven to play a significant role in the pathogenesis of virtually all acute and chronic liver disorders. Recent studies demonstrated the medical applications of miRNA in various phases of hepatic pathology. PPARs play a major role in regulating many signaling pathways involved in various metabolic disorders. Non-alcoholic fatty liver disease (NAFLD) is the most prevalent form of chronic liver disease in the world, encompassing a spectrum spanning from mild steatosis to severe non-alcoholic steatohepatitis (NASH). PPARs were found to be one of the major regulators in the progression of NAFLD. There is no recognized treatment for NAFLD, even though numerous clinical trials are now underway. NAFLD is a major risk factor for developing hepatocellular carcinoma (HCC), and its frequency increases as obesity and diabetes become more prevalent. Reprogramming anti-diabetic and anti-obesity drugs is an effective therapy option for NAFLD and NASH. Several studies have also focused on the role of ncRNAs in the pathophysiology of NAFLD. The regulatory effects of these ncRNAs make them a primary target for treatments and as early biomarkers. In this study, the main focus will be to understand the regulation of PPARs through ncRNAs and their role in NAFLD.

Ageing and Obesity Shared Patterns: From Molecular Pathogenesis to Epigenetics

In modern societies, ageing and obesity represent medical challenges for healthcare professionals and caregivers. Obesity and ageing share common features including the related cellular and molecular pathways as well as the impacts they have as risk factors for a variety of diseases and health problems. Both of these health problems also share exercise and a healthy lifestyle as the best therapeutic options. Importantly, ageing and obesity also have common epigenetic changes (histone modification, DNA methylation, noncoding RNAs, and chromatin remodeling) that are also impacted by exercise. This suggests that epigenetic pathways are among the mechanisms via which exercise induces its benefits, including ageing and obesity improvements. Exploring these interrelations and based on the fact that both ageing and obesity represent risk factors for each other, would lead to optimizing the available therapeutic approaches towards improved obesity management and healthy ageing.

Low-dose Bisphenol-A Promotes Epigenetic Changes at Pparγ Promoter in Adipose Precursor Cells

Exposure to endocrine-disrupting chemicals such as Bisphenol-A (BPA) is associated with an increase in obesity prevalence. Diet is the primary cause of human exposure to this contaminant. BPA promotes obesity by inducing adipocyte dysfunction and altering adipogenesis. Contradictory evidence and unanswered questions are reported in the literature concerning the BPA effects on adipogenesis. To clarify this issue, we tested the effects of prolonged low-dose BPA exposure on different phases of adipogenesis in committed 3T3L1 and uncommitted NIH3T3 preadipocytes. Our findings show that BPA effects on the adipogenesis are mediated by epigenetic mechanisms by reducing peroxisome proliferator-activated receptor gamma (Pparγ) promoter methylation in preadipocytes. Nevertheless, in BPA-exposed 3T3L1, Pparγ expression only transiently increases as lipid accumulation at day 4 of differentiation, without altering the adipogenic potential of the precursor cells. In the absence of differentiation mix, BPA does not make the 3T3L1 an in vitro model of spontaneous adipogenesis and the effects on the Pparγ expression are still limited at day 4 of differentiation. Furthermore, BPA exposure does not commit the NIH3T3 to the adipocyte lineage, although Pparγ overexpression is more evident both in preadipocytes and during the adipocyte differentiation. Interestingly, termination of the BPA exposure restores the Pparγ promoter methylation and inflammatory profile of the 3T3L1 cells. This study shows that BPA induces epigenetic changes in a key adipogenic gene. These modifications are reversible and do not affect preadipocyte commitment and/or differentiation. We identify an alternative transcriptional mechanism by which BPA affects gene expression and demonstrate how the challenge of preventing exposure is fundamental for human health.

Adipose Tissue Modification through Feeding Strategies and Their Implication on Adipogenesis and Adipose Tissue Metabolism in Ruminants

Dietary recommendations by health authorities have been advising of the importance of diminishing saturated fatty acids (SFA) consumption and replacing them by polyunsaturated fatty acids (PUFA), particularly omega-3. Therefore, there have been efforts to enhance food fatty acid profiles, helping them to meet human nutritional recommendations. Ruminant meat is the major dietary conjugated linoleic acid (CLA) source, but it also contains SFA at relatively high proportions, deriving from ruminal biohydrogenation of PUFA. Additionally, lipid metabolism in ruminants may differ from other species. Recent research has aimed to modify the fatty acid profile of meat, and other animal products. This review summarizes dietary strategies based on the n-3 PUFA supplementation of ruminant diets and their effects on meat fatty acid composition. Additionally, the role of n-3 PUFA in adipose tissue (AT) development and in the expression of key genes involved in adipogenesis and lipid metabolism is discussed. It has been demonstrated that linseed supplementation leads to an increase in α-linolenic acid (ALA) and eicosapentaenoic acid (EPA), but not in docosahexaenoic acid (DHA), whilst fish oil and algae increase DHA content. Dietary PUFA can alter AT adiposity and modulate lipid metabolism genes expression, although further research is required to clarify the underlying mechanism.

Therapeutic Effect of Seaweed Derived Xanthophyl Carotenoid on Obesity Management; Overview of the Last Decade

Present-day lifestyles associated with high calorie-fat intake and accumulation, as well as energy imbalance, have led to the development of obesity and its comorbidities, which have emerged as some of the major health issues globally. To combat the disease, many studies have reported the anti-obesity effects of natural compounds in foods, with some advantages over chemical treatments. Carotenoids, such as xanthophyll derived from seaweeds, have attracted the attention of researchers due to their notable biological activities, which are associated mainly with their antioxidant properties. Their involvement in oxidative stress modulation, the regulation of major transcription factors and enzymes, and their antagonistic effects on various obesity parameters have been examined in both in vitro and in vivo studies. The present review is a collation of published research over the last decade on the antioxidant properties of seaweed xanthophyll carotenoids, with a focus on fucoxanthin and astaxanthin and their mechanisms of action in obesity prevention and treatment.

Comparative effects of nanoemulsions loaded with duck oil and lard oil on palmitate-induced lipotoxicity

The effects of duck oil and lard oil on lipotoxicity induced by saturated long-chain fatty acids were evaluated in HepG2 cells. Lipotoxicity triggered by palmitate, a saturated fatty acid, was inhibited more by duck oil-loaded nanoemulsion (DO-NE) than by lard oil-loaded nanoemulsion (LO-NE) and control nanoemulsion (NE) in HepG2 cells. Accumulation of reactive oxygen species and lipid vacuoles in HepG2 cells induced by palmitate treatment was inhibited by DO-NE but not by LO-NE. Consistently, treatment of HepG2 cells with DO-NE, but not with NE or LO-NE, significantly reduced the expression levels of peroxisome proliferator-activated receptor-γ2 and sterol regulatory element-binding protein-1, which are key regulatory proteins in hepatic lipid accumulation. In addition, the cleavage of poly (ADP-ribose) polymerase and caspase-3 were reduced more by DO-NE than by LO-NE, indicating that DO-NE directly attenuates cellular damage induced by palmitate. Collectively, these results imply that the biological activity of duck oil against palmitate-induced cellular damage is more potent than that of lard oil. PRACTICAL APPLICATIONS: Accumulated lipids in nonadipose tissues, especially the liver, cause lipotoxicity, a pathologic feature of hepatic disorders, by inducing oxidative stress. A nanoemulsion loaded with duck oil, which is a functional food widely consumed by Korean people, inhibited lipotoxicity by suppressing lipid accumulation in HepG2 cells exposed to palmitate, which mimic nonalcoholic fatty liver disease. Thus, we propose that duck oil can be used as a functional food to improve lipid-induced hepatic disorders.

Cellular prion protein regulates the differentiation and function of adipocytes through autophagy flux

The role of autophagy modulation in adipogenic differentiation and the possible autophagy modulators targeting adipogenesis remain unclear. In this study, we investigated whether normal cellular prion protein (PrP<C>) is involved in the modulation of autophagy and affects adipogenic differentiation in vivo and in vitro. Surprisingly, autophagy flux signals were activated in the adipose tissue of prion protein-deficient mice and PrP<C>-deleted 3T3-L1 adipocytes. The activation of autophagy flux mediated by PrP<C> deletion was confirmed in the adipose tissue via transmission electron microscopy. Adipocyte differentiation factors were highly induced in prion protein-deficient adipose tissue and 3T3-L1 adipocytes. In addition, deletion of prion protein significantly increased visceral fat volume, body fat weight, adipocyte cell size, and body weight gain in Prnp-knockout mice and increased lipid accumulation in PrP<C> siRNA-transfected 3T3-L1 cells. However, the overexpression of prion protein using adenovirus inhibited the autophagic flux signals, lipid accumulation, and the PPAR-γ and C/EBP-α mRNA and protein expression levels in comparison to those in the control cells. Our results demonstrated that deletion of normal prion protein accelerated adipogenic differentiation and lipid accumulation mediated via autophagy flux activation.

Nanoemulsions improve the efficacy of turmeric in palmitate- and high fat diet-induced cellular and animal models

Turmeric is a well-known functional food exhibiting multiple biological activities in health and disease. However, low aqueous solubility and poor bioavailability limit its therapeutic potential. Herein, we investigated the utility of nanoemulsions as a carrier to improve the efficacy of turmeric. Compared with turmeric extract (TE), 5% TE-loaded nanoemulsion (TE-NE), which contains 20-fold lower curcumin content than TE, achieved similar inhibition of palmitate-induced lipotoxicity in HepG2 cells. Exposure of HepG2 cells to 5% TE-NE also suppressed the palmitate-induced accumulation of lipid vacuoles and reactive oxygen species comparably with TE, and was accompanied by decreased levels of sterol regulatory element-binding protein (SREBP)-1, peroxisome proliferator-activated receptor-γ2 (PPAR-γ2), cleaved caspase-3, and poly (ADP-ribose) polymerase (PARP). Consistent with these effects in HepG2 cells, oral administration of 5% TE-NE to mice fed a high fat diet (HFD) markedly suppressed lipid accumulation in liver, leading to a significant reduction in body weight and adipose tissue weight, equivalent to the effects observed with TE. Compared with TE, 5% TE-NE also equivalently inhibited the levels of SREBP-1, PPAR-γ2, cleaved caspase-3, and PARP in the liver of mice fed a HFD. Furthermore, TE and 5% TE-NE significantly improved serum lipid profiles in a similar manner. These observations indicate that nanoemulsions can improve the efficacy of turmeric, thereby eliciting more potent biological efficacy against palmitate- and high fat diet (HFD)-induced cellular damage.

Targeting Peroxisome Proliferator-Activated Receptor γ to Increase Estrogen-Induced Apoptosis in Estrogen-Deprived Breast Cancer Cells

Peroxisome proliferator-activated receptor γ (PPARγ) is an important transcription factor that modulates lipid metabolism and inflammation. However, it remains unclear whether PPARγ is involved in modulation of estrogen (E₂)-induced inflammation, thus affecting apoptosis of E₂-deprived breast cancer cells, MCF-7:5C and MCF-7:2A. Here, we demonstrated that E₂ treatment suppressed the function of PPARγ in both cell lines, although the suppressive effect in MCF-7:2A cells was delayed owing to high PPARγ expression. Activation of PPARγ by a specific agonist, pioglitazone, selectively blocked the induction of TNFα expression by E₂, but did not affect other adipose inflammatory genes, such as fatty acid desaturase 1 and IL6. This suppression of TNFα expression by pioglitazone was mainly mediated by transrepression of nuclear factor-κB (NF-κB) DNA-binding activity. A novel finding was that NF-κB functions as an oxidative stress inducer in MCF-7:5C cells but an antioxidant in MCF-7:2A cells. Therefore, the NF-κB inhibitor JSH-23 displayed effects equivalent to those of pioglitazone, with complete inhibition of apoptosis in MCF-7:5C cells, but it increased E₂-induced apoptosis in MCF-7:2A cells. Depletion of PPARγ by siRNA or the PPARγ antagonist T0070907 accelerated E₂-induced apoptosis, with activation of NF-κB-dependent TNFα and oxidative stress. For the first time, we demonstrated that PPARγ is a growth signal and has potential to modulate NF-κB activity and oxidative stress in E₂-deprived breast cancer cell lines. All of these findings suggest that anti-PPARγ therapy is a novel strategy to improve the therapeutic effects of E₂-induced apoptosis in E₂-deprived breast cancer.

Effects of dietary n-6: n-3 polyunsaturated fatty acid ratios on meat quality, carcass characteristics, tissue fatty acid profiles, and expression of lipogenic genes in growing goats

The present study was conducted to investigate the effects of altering the ratio of n-6 to n-3 fatty acids in the diet on meat quality, fatty acid composition of muscle, and expression of lipogenic genes in the muscle of Boer goats. A total of twenty-one Boer goats (5 months old; 31.66±1.07 kg body weight) were randomly assigned to three dietary treatments with n-6:n-3 fatty acid ratios of 2.27:1 (LR), 5.01:1 (MR) and 10.38:1 (HR), fed at 3.7% of body weight. After 100 days of feeding, all goats were slaughtered and the longissimus dorsi muscle was sampled for analysis of fatty acids and gene expression. The dietary treatments did not affect (P>0.05) the carcass traits, and meat quality of growing goats. The concentrations of cis-9,trans-11 conjugated linoleic acid, trans vaccenic acid, polyunsaturated fatty acids, and unsaturated/saturated fatty acid ratios linearly increased (P<0.01) with decreasing dietary n-6:n-3 fatty acid ratios, especially for LR in the longissimus dorsi muscle of goats. In contrast, the mRNA expression level of the PPARα and PPARγ was down-regulated and stearoyl-CoA desaturase up-regulated in the longissimus dorsi of growing goats with increasing dietary n-6:n-3 fatty acid ratios (P<0.01). In conclusion, the results obtained indicate that the optimal n-6:n-3 fatty acid ratio of 2.27:1 exerted beneficial effects on meat fatty acid profiles, leading towards an enrichment in n-3 polyunsaturated fatty acids and conjugated linoleic acid in goat intramuscular fat.

Anti-cancer Effects of MW-03, a Novel Indole Compound, by Inducing 15-Hydroxyprostaglandin Dehydrogenase and Cellular Growth Inhibition in the LS174T Human Colon Cancer Cell Line

Increases in the expression of prostaglandin E₂ (PGE₂) are widely known to be involved in aberrant growth in the early stage of colon cancer development. We herein demonstrated that the novel indole compound MW-03 reduced PGE₂-induced cAMP formation by catalization to an inactive metabolite by inducing 15-hydroxyprostaglandin dehydrogenase through the activation of peroxisome proliferator-activated receptor-γ. MW-03 also inhibited colon cancer cell growth by arresting the cell cycle at the S phase. Although the target of MW-03 for cell cycle inhibition has not yet been identified, these dual anti-cancer effects of MW-03 itself and/or its leading compound(s) on colon cancer cells may reduce colon cancer development and, thus, have potential as a novel treatment for the early stage of this disease.

The RBM14/CoAA-interacting, long intergenic non-coding RNA Paral1 regulates adipogenesis and coactivates the nuclear receptor PPARγ

Adipocyte differentiation and function relies on a network of transcription factors, which is disrupted in obesity-associated low grade, chronic inflammation leading to adipose tissue dysfunction. In this context, there is a need for a thorough understanding of the transcriptional regulatory network involved in adipose tissue pathophysiology. Recent advances in the functional annotation of the genome has highlighted the role of non-coding RNAs in cellular differentiation processes in coordination with transcription factors. Using an unbiased genome-wide approach, we identified and characterized a novel long intergenic non-coding RNA (lincRNA) strongly induced during adipocyte differentiation. This lincRNA favors adipocyte differentiation and coactivates the master adipogenic regulator peroxisome proliferator-activated receptor gamma (PPARγ) through interaction with the paraspeckle component and hnRNP-like RNA binding protein 14 (RBM14/NCoAA), and was therefore called PPARγ-activator RBM14-associated lncRNA (Paral1). Paral1 expression is restricted to adipocytes and decreased in humans with increasing body mass index. A decreased expression was also observed in diet-induced or genetic mouse models of obesity and this down-regulation was mimicked in vitro by TNF treatment. In conclusion, we have identified a novel component of the adipogenic transcriptional regulatory network defining the lincRNA Paral1 as an obesity-sensitive regulator of adipocyte differentiation and function.

Short-chain fatty acids and inulin, but not guar gum, prevent diet-induced obesity and insulin resistance through differential mechanisms in mice

The role of dietary fibre and short-chain fatty acids (SCFA) in obesity development is controversially discussed. Here, we investigated how various types of dietary fibre and different SCFA ratios affect metabolic syndrome-related disorders. Male mice (B6) were fed high-fat diets supplemented with dietary fibres (either cellulose, inulin or guar gum) or different Ac:Pr ratios (high acetate (HAc) or propionate (HPr)) for 30 weeks. Body-fat gain and insulin resistance were greatly reduced by inulin, but not by guar gum, and completely prevented by SCFA supplementation. Only inulin and HAc increased body temperature, possibly by the induction of beige/browning markers in WAT. In addition, inulin and SCFA lowered hepatic triglycerides and improved insulin sensitivity. Both, inulin and HAc reduced hepatic fatty acid uptake, while only inulin enhanced mitochondrial capacity and only HAc suppressed lipogenesis in liver. Interestingly, HPr was accompanied by the induction of Nrg4 in BAT. Fermentable fibre supplementation increased the abundance of bifidobacteria; B. animalis was particularly stimulated by inulin and B. pseudolongum by guar gum. We conclude that in contrast to guar gum, inulin and SCFA prevent the onset of diet-induced weight gain and hepatic steatosis by different mechanisms on liver and adipose tissue metabolism.

Fish collagen peptide inhibits the adipogenic differentiation of preadipocytes and ameliorates obesity in high fat diet-fed mice

Bioactivities of fish collagen peptide are now being elucidated in diverse biological systems. Here, we investigated the effect of fish collagen peptide on the adipogenic differentiation of 3T3-L1 preadipocytes and in obese mice fed a high fat diet (HFD). Subcritical water-hydrolyzed fish collagen peptide (SWFCP) significantly inhibited lipid accumulation during the differentiation of 3T3-L1 preadipocytes, which was accompanied by decreased expression of CCAAT-enhancer-binding protein-α (C/EBP-α), peroxisome proliferator-activated receptor-γ (PPAR-γ), and adipocyte protein 2 (aP2) genes, key regulators of differentiation and maintenance of adipocytes. SWFCP was also found to suppress the palmitate-induced accumulation of lipid vacuoles in hepatocytes. Oral administration of SWFCP significantly reduced HFD-induced body weight gain without a significant difference in food intake. Consistent with its effects in 3T3-L1 preadipocytes, SWFCP inhibited the expression of C/EBP-α, PPAR-γ, and aP2 in epididymal adipose tissue of mice fed a HFD, leading to a significant reduction in adipocyte size. Furthermore, SWFCP significantly reduced serum levels of total cholesterol, triglyceride, and low-density lipoprotein, and increased serum high-density lipoprotein. These observations suggest that SWFCP inhibits adipocyte differentiation through a mechanism involving transcriptional repression of the major adipogenic regulators C/EBP-α and PPAR-γ, thereby reducing body weight gain and adipogenesis in an animal model of obesity.

Effects of Angelica dahurica on obesity and fatty liver in mice

Angelica dahurica (A. dahurica) is a traditional Chinese medicinal plant being used in clinical practice. The present study demonstrated that A. dahurica could reduce white-fat weight in high-fat-diet hyperlipidemic mice, decrease total cholesterol and triglyceride concentrations in the livers of both high-fat-diet and Triton WR1339 induced hyperlipidemic mice, and enhance the total hepatic lipase activities of them. These findings were further supported by the results derived from the experiments with HepG2 cells in vitro. In addition, the proteins related to lipids metabolism were investigated using LC-MS/MS, indicating that genes of lipid metabolism and lipid transport were regulated by A. dhurica. The results from LC-MS/MS were further conformed by Western blot and real time PCR assays. A. dahurica could down-regulate the expression of catalase (CAT) and sterol carrier protein2 (SCP2) and up-regulate the expression of lipid metabolism related genes-lipase member C (LIPC) and peroxisome proliferator-activated receptor gamma (PPARγ). In the Triton WR1339 mouse liver and HepG2 cells in vitro, A. dahurica was able to increase the expression of LIPC and PPARγ, confirming the results from in vivo experiments. Imperatorin showed the same activity as A. dahurica, suggesting it was one of the major active ingredients of the herb. In conclusion, our work represented a first investigation demonstrating that A. dahurica was able to regulate lipid metabolism and could be developed as a novel approach to fighting against fatty liver and obesity.

Pioglitazone Effect on Glioma Stem Cell Lines: Really a Promising Drug Therapy for Glioblastoma?

Glioblastoma multiforme (GBM) represents one of the most frequent malignant brain tumors. Current therapies do not provide real solutions to this pathology. Their failure can be ascribed to a cell subpopulation with stem-like properties called glioma stem cells (GSCs). Therefore, new therapeutic strategies GSC-targeted are needed. PPARγ, a nuclear receptor involved in lipid metabolism, has already been indicated as a promising target for antineoplastic therapies. Recent studies have reported that synthetic PPARγ agonists, already in clinical use for the treatment of type II diabetes, exhibit antineoplastic effects in a wide range of malignant tumor cells, including glioma cells. We investigated the effect of the synthetic PPARγ agonist Pioglitazone on viability, proliferation, morphology, and differentiation in six GSC lines isolated from GBM patients. We also analyzed Pioglitazone-induced changes in transcriptional levels of Wnt/β catenin related genes. Results showed that response to Pioglitazone was heterogeneous inducing an evident decrease of cell viability and proliferation only in a subset of GSC lines. We did not find any sign of cell differentiation neither observing cell morphology nor analyzing the expression of stemness and differentiation markers. Moreover, Wnt/β signaling pathway was only mildly affected from a transcriptional point of view after Pioglitazone exposure.

The ubiquitous transcription factor CTCF promotes lineage-specific epigenomic remodeling and establishment of transcriptional networks driving cell differentiation

Cell differentiation relies on tissue-specific transcription factors (TFs) that cooperate to establish unique transcriptomes and phenotypes. However, the role of ubiquitous TFs in these processes remains poorly defined. Recently, we have shown that the CCCTC-binding factor (CTCF) is required for adipocyte differentiation through epigenomic remodelling of adipose tissue-specific enhancers and transcriptional activation of Peroxisome proliferator-activated receptor gamma (PPARG), the main driver of the adipogenic program (PPARG), and its target genes. Here, we discuss how these findings, together with the recent literature, illuminate a functional role for ubiquitous TFs in lineage-determining transcriptional networks.

In vitro reversion of activated primary human hepatic stellate cells

Background

Liver fibrosis is characterized by the excessive formation and accumulation of matrix proteins as a result of wound healing in the liver. A main event during fibrogenesis is the activation of the liver resident quiescent hepatic stellate cell (qHSC). Recent studies suggest that reversion of the activated HSC (aHSC) phenotype into a quiescent-like phenotype could be a major cellular mechanism underlying fibrosis regression in the liver, thereby offering new therapeutic perspectives for the treatment of liver fibrosis. Whether human HSCs have the ability to undergo a similar reversion in phenotype is currently unknown. The aim of the present study is to identify experimental conditions that can revert the in vitro activated phenotype of primary human HSCs and consequently to map the molecular events associated with this reversion process by gene expression profiling.

Results

We find that epidermal growth factor (EGF) and fibroblast growth factor 2 (FGF2) synergistically downregulate the expression of ACTA2 and LOX in primary human aHSCs. Their combination with oleic acid, palmitic acid, and retinol further potentiates a more quiescent-like phenotype as demonstrated by the abundant presence of retinyl ester-positive intra-cytoplasmic lipid droplets, low expression levels of activation markers, and a reduced basal as well as cytokine-stimulated proliferation and matrix metalloproteinase activity. Gene expression profiling experiments reveal that these in vitro reverted primary human HSCs (rHSCs) display an intermediary phenotype that is distinct from qHSCs and aHSCs. Interestingly, this intermediary phenotype is characterized by the increased expression of several previously identified signature genes of in vivo inactivated mouse HSCs such as CXCL1, CXCL2, and CTSS, suggesting also a potential role for these genes in promoting a quiescent-like phenotype in human HSCs.

Conclusions

We provide evidence for the ability of human primary aHSCs to revert in vitro to a transitional state through synergistic action of EGF, FGF2, dietary fatty acids and retinol, and provide a first phenotypic and genomic characterization of human in vitro rHSCs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13069-015-0031-z) contains supplementary material, which is available to authorized users.

Epigenetic Activity of Peroxisome Proliferator-Activated Receptor Gamma Agonists Increases the Anticancer Effect of Histone Deacetylase Inhibitors on Multiple Myeloma Cells

Epigenetic modifications play a major role in the development of multiple myeloma. We have previously reported that the PPARγ agonist pioglitazone (PIO) enhances, in-vitro, the cytotoxic effect of the Histone deacetylase inhibitor (HDACi), valproic acid (VPA), on multiple myeloma cells. Here, we described the development of a new multiple myeloma mouse model using MOLP8 cells, in order to evaluate the effect of VPA/PIO combination on the progression of myeloma cells, by analyzing the proliferation of bone marrow plasma cells. We showed that VPA/PIO delays the progression of the disease and the invasion of myeloma cells in the bone marrow. Mechanistically, we demonstrated that VPA/PIO increases the cleavage of caspase 3 and PARP, and induces the acetylation of Histone 3 (H3). Furthermore, we provided evidence that PPARγ agonist is able to enhance the action of other HDACi such as Vorinostat or Mocetinostat. Using PPARγ antagonist or siPPARγ, we strongly suggest that, as described during adipogenesis, PIO behaves as an epigenetic regulator by improving the activity of HDACi. This study highlights the therapeutic benefit of PIO/VPA combination, compared to VPA treatment as a single-arm therapy on multiple myeloma and further highlights that such combination may constitute a new promising treatment strategy which should be supported by clinical trials.

The effect of polyunsaturated fatty acids on obesity through epigenetic modifications

BACKGROUND AND PURPOSE

In recent years it has been demonstrated that polyunsaturated fatty acids (PUFA) have anti-inflammatory and as regulators of lipid metabolism. However, the epigenomic mechanisms involved in these processes are not known in depth. The aim of this review was to describe the scientific evidence supports that regular consumption of PUFA may reduce obesity and overweight by altering epigenetic marks.

MATERIAL AND METHODS

A search of recent publications was carried out in human clinical trials, as well as animal model and in vitro experiments.

RESULTS

Exist a possible therapeutic effect of PUFAs on the prevention and development of obesity due to their ability to reversively modify the methylation of the promoters of genes associated with lipid metabolism and to modulate the activity of certain microRNAs.

CONCLUSIONS

A better knowledge and understanding of the PUFAs role in epigenetic regulation of obesity is possible with the current published results. The PUFAs may modulate the promotor epigenetic marks in several adipogenic genes and regulate the expression of several miRNAs.

The E3 ubiquitin ligase TRIM23 regulates adipocyte differentiation via stabilization of the adipogenic activator PPARγ

Adipocyte differentiation is a strictly controlled process regulated by a series of transcriptional activators. Adipogenic signals activate early adipogenic activators and facilitate the transient formation of early enhanceosomes at target genes. These enhancer regions are subsequently inherited by late enhanceosomes. PPARγ is one of the late adipogenic activators and is known as a master regulator of adipogenesis. However, the factors that regulate PPARγ expression remain to be elucidated. Here, we show that a novel ubiquitin E3 ligase, tripartite motif protein 23 (TRIM23), stabilizes PPARγ protein and mediates atypical polyubiquitin conjugation. TRIM23 knockdown caused a marked decrease in PPARγ protein abundance during preadipocyte differentiation, resulting in a severe defect in late adipogenic differentiation, whereas it did not affect the formation of early enhanceosomes. Our results suggest that TRIM23 plays a critical role in the switching from early to late adipogenic enhanceosomes by stabilizing PPARγ protein possibly via atypical polyubiquitin conjugation.

DOI:http://dx.doi.org/10.7554/eLife.05615.001

The world is facing a global epidemic of obesity, which also increases the risk for diabetes and heart disease. Obesity is caused when excess fat is stored in fat cells, and overweight individuals have larger fat cells compared to healthy weight people. Therefore understanding how fat cells are created in the body can provide new ways to combat obesity.

Fat cells, also known as adipocytes, arise from precursor cells via a process called adipogenesis. This requires the activity of proteins called transcription factors that bind to DNA and switch on the expression of genes. PPARγ is an important transcription factor that drives the expression of the genes that are needed to convert a precursor cell to a mature adipocyte.

For adipogenesis to proceed, cells have to maintain the appropriate levels of PPARγ. If the amount of PPARγ bound to DNA is too low, then it is unable to activate gene expression. However, the mechanisms by which cells maintain the correct levels of PPARγ activity remain poorly understood. Watanabe et al. analyzed this process in mouse cells and identified a protein called TRIM23 that is produced in precursor cells. Cells in which the levels of TRIM23 were artificially lowered failed to mature into fat cells; this suggests that this protein is necessary for adipogenesis. Furthermore, in the absence of TRIM23, the amount of PPARγ that occupied regions of DNA was also markedly reduced. A direct consequence of this was a decline in the expression of several genes that are required for the later steps in the adipogenesis process.

Watanabe et al. next analyzed the mechanism through which TRIM23 had an effect on the levels of PPARγ. It is known from previous work that TRIM23 belongs to a family of enzymes that attach a small molecular tag called ubiquitin onto other proteins. This ubiquitin tag typically marks these proteins for rapid destruction by a large molecular machine called the proteasome. Watanabe et al. found that TRIM23 also modified PPARγ with ubiquitin, but that it did so in an unusual manner that instead prevented the proteasome from recognizing PPARγ and destroying it. As such, TRIM23 stabilizes the levels of PPARγ in cells.

By providing new insights into how adipogenesis is regulated, these findings suggest that TRIM23 may be a potential therapeutic target in the treatment of diabetes and disorders related to obesity.

DOI:http://dx.doi.org/10.7554/eLife.05615.002

A dynamic CTCF chromatin binding landscape promotes DNA hydroxymethylation and transcriptional induction of adipocyte differentiation

CCCTC-binding factor (CTCF) is a ubiquitously expressed multifunctional transcription factor characterized by chromatin binding patterns often described as largely invariant. In this context, how CTCF chromatin recruitment and functionalities are used to promote cell type-specific gene expression remains poorly defined. Here, we show that, in addition to constitutively bound CTCF binding sites (CTS), the CTCF cistrome comprises a large proportion of sites showing highly dynamic binding patterns during the course of adipogenesis. Interestingly, dynamic CTCF chromatin binding is positively linked with changes in expression of genes involved in biological functions defining the different stages of adipogenesis. Importantly, a subset of these dynamic CTS are gained at cell type-specific regulatory regions, in line with a requirement for CTCF in transcriptional induction of adipocyte differentiation. This relates to, at least in part, CTCF requirement for transcriptional activation of both the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARG) and its target genes. Functionally, we show that CTCF interacts with TET methylcytosine dioxygenase (TET) enzymes and promotes adipogenic transcriptional enhancer DNA hydroxymethylation. Our study reveals a dynamic CTCF chromatin binding landscape required for epigenomic remodeling of enhancers and transcriptional activation driving cell differentiation.

Impaired preadipocyte differentiation into adipocytes in subcutaneous abdominal adipose of PCOS-like female rhesus monkeys

Metabolic characteristics of polycystic ovary syndrome women and polycystic ovary syndrome-like, prenatally androgenized (PA) female monkeys worsen with age, with altered adipogenesis of sc abdominal adipose potentially contributing to age-related adverse effects on metabolism. This study examines whether adipocyte morphology and gene expression in sc abdominal adipose differ between late reproductive-aged PA female rhesus monkeys compared with age-matched controls (C). Subcutaneous abdominal adipose of both groups was obtained for histological imaging and mRNA determination of zinc finger protein 423 (Zfp423) as a marker of adipose stem cell commitment to preadipocytes, and CCAAT/enhancer binding protein (C/EBP)α/peroxisome proliferator-activated receptor (PPAR)δ as well as C/EBPα/PPARγ as respective markers of early- and late-stage differentiation of preadipocytes to adipocytes. In all females combined, serum testosterone (T) levels positively correlated with fasting serum levels of total free fatty acid (r(2) = 0.73, P < .002). PA females had a greater population of small adipocytes vs C (P < .001) in the presence of increased Zfp423 (P < .025 vs C females) and decreased C/EBPα (P < .003, vs C females) mRNA expression. Moreover, Zfp423 mRNA expression positively correlated with circulating total free fatty acid levels during iv glucose tolerance testing (P < .004, r(2) = 0.66), whereas C/EBPα mRNA expression negatively correlated with serum T levels (P < .02, r(2) = 0.43). Gene expression of PPARδ and PPARγ were comparable between groups (P = .723 and P = .18, respectively). Early-to-mid gestational T excess in female rhesus monkeys impairs adult preadipocyte differentiation to adipocytes in sc abdominal adipose and may constrain the ability of this adipose depot to safely store fat with age.

Peroxisome proliferator-activated receptor γ regulates genes involved in insulin/insulin-like growth factor signaling and lipid metabolism during adipogenesis through functionally distinct enhancer classes

The nuclear receptor peroxisome proliferator-activated receptor (PPAR) is a transcription factor whose expression is induced during adipogenesis and that is required for the acquisition and control of mature adipocyte functions. Indeed, PPAR induces the expression of genes involved in lipid synthesis and storage through enhancers activated during adipocyte differentiation. Here, we show that PPAR also binds to enhancers already active in preadipocytes as evidenced by an active chromatin state including lower DNA methylation levels despite higher CpG content. These constitutive enhancers are linked to genes involved in the insulin/insulin-like growth factor signaling pathway that are transcriptionally induced during adipogenesis but to a lower extent than lipid metabolism genes, because of stronger basal expression levels in preadipocytes. This is consistent with the sequential involvement of hormonal sensitivity and lipid handling during adipocyte maturation and correlates with the chromatin structure dynamics at constitutive and activated enhancers. Interestingly, constitutive enhancers are evolutionary conserved and can be activated in other tissues, in contrast to enhancers controlling lipid handling genes whose activation is more restricted to adipocytes. Thus, PPAR utilizes both broadly active and cell type-specific enhancers to modulate the dynamic range of activation of genes involved in the adipogenic process.

Modulation of NKG2D ligand expression and metastasis in tumors by spironolactone via RXRγ activation

The diuretic drug spironolactone up-regulates NKG2D ligand expression in colon cancer cells via activation of the ATM–Chk2–mediated checkpoint pathway to enhance the antitumor function of NK cells.

Tumor metastasis and lack of NKG2D ligand (NKG2DL) expression are associated with poor prognosis in patients with colon cancer. Here, we found that spironolactone (SPIR), an FDA-approved diuretic drug with a long-term safety profile, can up-regulate NKG2DL expression in multiple colon cancer cell lines by activating the ATM–Chk2-mediated checkpoint pathway, which in turn enhances tumor elimination by natural killer cells. SPIR can also up-regulate the expression of metastasis-suppressor genes TIMP2 and TIMP3, thereby reducing tumor cell invasiveness. Although SPIR is an aldosterone antagonist, its antitumor effects are independent of the mineralocorticoid receptor pathway. By screening the human nuclear hormone receptor siRNA library, we identified retinoid X receptor γ (RXRγ) instead as being indispensable for the antitumor functions of SPIR. Collectively, our results strongly support the use of SPIR or other RXRγ agonists with minimal side effects for colon cancer prevention and therapy.

On the TRAIL of obesity and diabetes

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) has been extensively studied for its preferential ability to induce apoptosis of cancer cells. Beyond the cytotoxic capacity of TRAIL, new physiological and pathological roles for TRAIL have been identified, and there is now growing evidence supporting its involvement in the development of obesity and diabetes. This review summarizes the most recent findings associating TRAIL with obesity and diabetes in both humans and experimental settings. We also present and discuss some of the reported controversies behind TRAIL signaling and function. Understanding TRAIL mechanism(s) in vivo and its involvement in disease may lead to novel strategies to combat the growing pandemic of obesity and diabetes worldwide.

Effect of linseed oil dietary supplementation on fatty acid composition and gene expression in adipose tissue of growing goats

This study was conducted to determine the effects of feeding oil palm frond silage based diets with added linseed oil (LO) containing high α-linolenic acid (C18:3n-3), namely, high LO (HLO), low LO (LLO), and without LO as the control group (CON) on the fatty acid (FA) composition of subcutaneous adipose tissue and the gene expression of peroxisome proliferator-activated receptor (PPAR)α, PPAR-γ, and stearoyl-CoA desaturase (SCD) in Boer goats. The proportion of C18:3n-3 in subcutaneous adipose tissue was increased (P < 0.01) by increasing the LO in the diet, suggesting that the FA from HLO might have escaped ruminal biohydrogenation. Animals fed HLO diets had lower proportions of C18:1 trans-11, C18:2n-6, CLA cis-9 trans-11, and C20:4n-6 and higher proportions of C18:3n-3, C22:5n-3, and C22:6n-3 in the subcutaneous adipose tissue than animals fed the CON diets, resulting in a decreased n-6:n-3 fatty acid ratio (FAR) in the tissue. In addition, feeding the HLO diet upregulated the expression of PPAR-γ (P < 0.05) but downregulated the expression of SCD (P < 0.05) in the adipose tissue. The results of the present study show that LO can be safely incorporated in the diets of goats to enrich goat meat with potential health beneficial FA (i.e., n-3 FA).