Overexpression and ribozyme-mediated targeting of transcriptional coactivators CREB-binding protein and p300 revealed their indispensable roles in adipocyte differentiation through the regulation of peroxisome proliferator-activated receptor gamma

Acetylation and deacetylation of histone in adipocyte differentiation and the potential significance in cancer

Adipocytes are derived from pluripotent mesenchymal stem cells and can develop into several cell types including adipocytes, myocytes, chondrocytes, and osteocytes. Adipocyte differentiation is regulated by a variety of transcription factors and signaling pathways. Various epigenetic factors, particularly histone modifications, play key roles in adipocyte differentiation and have indispensable functions in altering chromatin conformation. Histone acetylases and deacetylases participate in the regulation of protein acetylation, mediate transcriptional and post-translational modifications, and directly acetylate or deacetylate various transcription factors and regulatory proteins. The adipocyte differentiation of stem cells plays a key role in various metabolic diseases. Cancer stem cells(CSCs) play an important function in cancer metastasis, recurrence, and drug resistance, and have the characteristics of stem cells. They are expressed in various cell lineages, including adipocytes. Recent studies have shown that cancer stem cells that undergo epithelial-mesenchymal transformation can undergo adipocytic differentiation, thereby reducing the degree of malignancy. This opens up new possibilities for cancer treatment. This review summarizes the regulation of acetylation during adipocyte differentiation, involving the functions of histone acetylating and deacetylating enzymes as well as non-histone acetylation modifications. Mechanistic studies on adipogenesis and acetylation during the differentiation of cancer cells into a benign cell phenotype may help identify new targets for cancer treatment.

Inflammation-induced nitric oxide suppresses PPARα expression and function via downregulation of Sp1 transcriptional activity in adipocytes

The activation of peroxisome proliferator-activated receptor alpha (PPARα), a ligand-dependent transcription factor that regulates lipid oxidation-related genes, has been employed to treat hyperlipidemia. Emerging evidence indicates that Ppara gene expression decreases in adipose tissue under obese conditions; however, the underlying molecular mechanisms remain elusive. Here, we demonstrate that nitric oxide (NO) suppresses Ppara expression by regulating its promoter activity via suppression of specificity protein 1 (Sp1) transcriptional activity in adipocytes. NO derived from lipopolysaccharide (LPS) -activated macrophages or a NO donor (NOR5) treatment, suppressed Ppara mRNA expression in 10T1/2 adipocytes. In addition, Ppara transcript levels were reduced in the white adipose tissue (WAT) in both acute and chronic inflammation mouse models; however, such suppressive effects were attenuated via a nitric oxide synthase 2 (NOS2) inhibitor. Endoplasmic reticulum (ER) stress inhibitors attenuated the NO-induced repressive effects on Ppara gene expression in 10T1/2 adipocytes. Promoter mutagenesis and chromatin immunoprecipitation assays revealed that NO decreased the Sp1 occupancy in the proximal promoter regions of the Ppara gene, which might partially result from the reduced Sp1 expression levels by NO. This study delineated the molecular mechanism that modulates Ppara gene transcription upon NO stimulation in white adipocytes, suggesting a possible mechanism for the transcriptional downregulation of Ppara in WAT under obese conditions.

Knockdown of KLF7 inhibits the differentiation of both intramuscular and subcutaneous preadipocytes in goat

KLF7 belongs to the Krüppel-like factors (KLFs) family, which function as transcriptional regulators controlling a number of basic cellular processes, involving proliferation, differentiation, and migration. Here, we reveal insights into the differentiated expression of KLF7 in different goat tissues and different stages of growth, and the inhibition role of KLF7 knockdown to differentiation by using goat intramuscular and subcutaneous preadipocytes. We demonstrate that KLF7 expression is obviously changed during the differentiation of preadipocytes into mature adipocytes. Knockdown of KLF7 inhibited lipid droplet accumulation, reduced the expression of adipogenic markers both in intramuscular and subcutaneous preadipocytes in goats, suggesting that KLF7 is a novel regulator of adipogenesis. KLF7 expression changed also up or down-regulation the other KLF family members, but there were differences between these two types of cells. Investigation into the mechanism that KLF7 regulates preadipocyte differentiation revealed that KLF family members KLF1, KLF5, KLF6, KLF8, KLF11, KLF12, KLF16, KLF17 and adipogenic markers C/EBPα and SREBP1 promoter region present KLF7 transcriptional binding sites. Altogether, the data here identify KLF7 as a novel regulator of adipogenesis.

PPARγ in Atherosclerotic Endothelial Dysfunction: Regulatory Compounds and PTMs

The formation of atherosclerotic plaques is one of the main sources of cardiovascular disease. In addition to known risk factors such as dyslipidemia, diabetes, obesity, and hypertension, endothelial dysfunction has been shown to play a key role in the formation and progression of atherosclerosis. Peroxisome proliferator-activated receptor-gamma (PPARγ), a transcription factor belonging to the steroid superfamily, is expressed in the aorta and plays a critical role in protecting endothelial function. It thereby serves as a target for treating both diabetes and atherosclerosis. Although many studies have examined endothelial cell disorders in atherosclerosis, the role of PPARγ in endothelial dysfunction is still not well understood. In this review, we summarize the possible mechanisms of action behind PPARγ regulatory compounds and post-translational modifications (PTMs) of PPARγ in the control of endothelial function. We also explore the potential use of endothelial PPARγ-targeted agents in the prevention and treatment of atherosclerosis.

Molecular and cellular regulation of thermogenic fat

Thermogenic fat, consisting of brown and beige adipocytes, dissipates energy in the form of heat, in contrast to the characteristics of white adipocytes that store energy. Increasing energy expenditure by activating brown adipocytes or inducing beige adipocytes is a potential therapeutic strategy for treating obesity and type 2 diabetes. Thus, a better understanding of the underlying mechanisms of thermogenesis provides novel therapeutic interventions for metabolic diseases. In this review, we summarize the recent advances in the molecular regulation of thermogenesis, focusing on transcription factors, epigenetic regulators, metabolites, and non-coding RNAs. We further discuss the intercellular and inter-organ crosstalk that regulate thermogenesis, considering the heterogeneity and complex tissue microenvironment of thermogenic fat.

Protein posttranslational modifications in health and diseases: Functions, regulatory mechanisms, and therapeutic implications

Protein posttranslational modifications (PTMs) refer to the breaking or generation of covalent bonds on the backbones or amino acid side chains of proteins and expand the diversity of proteins, which provides the basis for the emergence of organismal complexity. To date, more than 650 types of protein modifications, such as the most well-known phosphorylation, ubiquitination, glycosylation, methylation, SUMOylation, short-chain and long-chain acylation modifications, redox modifications, and irreversible modifications, have been described, and the inventory is still increasing. By changing the protein conformation, localization, activity, stability, charges, and interactions with other biomolecules, PTMs ultimately alter the phenotypes and biological processes of cells. The homeostasis of protein modifications is important to human health. Abnormal PTMs may cause changes in protein properties and loss of protein functions, which are closely related to the occurrence and development of various diseases. In this review, we systematically introduce the characteristics, regulatory mechanisms, and functions of various PTMs in health and diseases. In addition, the therapeutic prospects in various diseases by targeting PTMs and associated regulatory enzymes are also summarized. This work will deepen the understanding of protein modifications in health and diseases and promote the discovery of diagnostic and prognostic markers and drug targets for diseases.

HPV E6 regulates therapy responses in oropharyngeal cancer by repressing the PGC-1α/ERRα axis

Therapy with radiation plus cisplatin kills HPV+ oropharyngeal squamous cell carcinomas (OPSCCs) by increasing reactive oxygen species beyond cellular antioxidant capacity. To explore why these standard treatments fail for some patients, we evaluated whether the variation in HPV oncoprotein levels among HPV+ OPSCCs affects mitochondrial metabolism, a source of antioxidant capacity. In cell line and patient-derived xenograft models, levels of HPV full-length E6 (fl-E6) inversely correlated with oxidative phosphorylation, antioxidant capacity, and therapy resistance, and fl-E6 was the only HPV oncoprotein to display such correlations. Ectopically expressing fl-E6 in models with low baseline levels reduced mitochondrial mass, depleted antioxidant capacity, and sensitized to therapy. In this setting, fl-E6 repressed the peroxisome proliferator-activated receptor gamma co-activator 1α/estrogen-related receptor α (PGC-1α/ERRα) pathway for mitochondrial biogenesis by reducing p53-dependent PGC-1α transcription. Concordant observations were made in 3 clinical cohorts, where expression of mitochondrial components was higher in tumors of patients with reduced survival. These tumors contained the lowest fl-E6 levels, the highest p53 target gene expression, and an activated PGC-1α/ERRα pathway. Our findings demonstrate that E6 can potentiate treatment responses by depleting mitochondrial antioxidant capacity and provide evidence for low E6 negatively affecting patient survival. E6's interaction with the PGC-1α/ERRα axis has implications for predicting and targeting treatment resistance in OPSCC.

Novel prospects for scarless wound healing: The roles of myofibroblasts and adipocytes

Disturbances or defects in the process of wound repair can disrupt the delicate balance of cells and molecules necessary for complete wound healing, thus leading to chronic wounds or fibrotic scars. Myofibroblasts are one of the most important cells involved in fibrotic scars, and reprogramming provides a potential avenue to increase myofibroblast clearance. Although myofibroblasts have long been recognized as terminally differentiated cells, recent studies have shown that myofibroblasts have the capacity to be reprogrammed into adipocytes. This review intends to summarize the potential of reprogramming myofibroblasts into adipocytes. We will discuss myofibroblast lineage tracing, as well as the known mechanisms underlying adipocyte regeneration from myofibroblasts. In addition, we investigated different changes in myofibroblast gene expression, transcriptional regulators, signalling pathways and epigenetic regulators during skin wound healing. In the future, myofibroblast reprogramming in wound healing will be better understood and appreciated, which may provide new ideas for the treatment of scarless wound healing.

An obesogenic feedforward loop involving PPARγ, acyl-CoA binding protein and GABAA receptor

Acyl-coenzyme-A-binding protein (ACBP), also known as a diazepam-binding inhibitor (DBI), is a potent stimulator of appetite and lipogenesis. Bioinformatic analyses combined with systematic screens revealed that peroxisome proliferator-activated receptor gamma (PPARγ) is the transcription factor that best explains the ACBP/DBI upregulation in metabolically active organs including the liver and adipose tissue. The PPARγ agonist rosiglitazone-induced ACBP/DBI upregulation, as well as weight gain, that could be prevented by knockout of Acbp/Dbi in mice. Moreover, liver-specific knockdown of Pparg prevented the high-fat diet (HFD)-induced upregulation of circulating ACBP/DBI levels and reduced body weight gain. Conversely, knockout of Acbp/Dbi prevented the HFD-induced upregulation of PPARγ. Notably, a single amino acid substitution (F77I) in the γ2 subunit of gamma-aminobutyric acid A receptor (GABA_AR), which abolishes ACBP/DBI binding to this receptor, prevented the HFD-induced weight gain, as well as the HFD-induced upregulation of ACBP/DBI, GABA_AR γ2, and PPARγ. Based on these results, we postulate the existence of an obesogenic feedforward loop relying on ACBP/DBI, GABA_AR, and PPARγ. Interruption of this vicious cycle, at any level, indistinguishably mitigates HFD-induced weight gain, hepatosteatosis, and hyperglycemia.

Tamarixetin Abrogates Adipogenesis Through Inhibiting p300/CBP-Associated Factor Acetyltransferase Activity in 3T3-L1 Preadipocyte Cells

Tamarixetin (TX) is an O-methylated flavonoid naturally derived from quercetin. TX has bioactive properties; however, whether it shows antilipogenic activity remains unknown. Therefore, in the present study, we aimed to determine the antilipogenic effects of TX using 3T3-L1 adipocytes. The 3T3-L1 adipocytes were cultured in a differentiation medium with or without TX. Lipid accumulation was diminished and the mRNA expression of lipogenesis-related genes was decreased following TX treatment. We found that TX exhibited antilipogenic effects by inhibiting the expression of p300/CBP-associated factor (pCAF), a histone acetyltransferase, as confirmed by pCAF knockdown. Furthermore, TX inhibited both pCAF expression and its activity, thereby reducing the total acetylation level of nonhistone and histone proteins. Finally, TX decreased the expression of CCAAT/enhancer-binding protein alpha and beta (CEBPα and CEBPβ), and peroxisome proliferator-activated receptor γ along with pCAF expression during adipogenesis of 3T3-L1 cells in a time-dependent manner. Collectively, our findings suggest that TX is a potent antilipogenic agent derived from natural products and may be used as a pCAF inhibitor.

The Potential to Fight Obesity with Adipogenesis Modulating Compounds

Obesity is an increasingly severe public health problem, which brings huge social and economic burdens. Increased body adiposity in obesity is not only tightly associated with type 2 diabetes, but also significantly increases the risks of other chronic diseases including cardiovascular diseases, fatty liver diseases and cancers. Adipogenesis describes the process of the differentiation and maturation of adipocytes, which accumulate in distributed adipose tissue at various sites in the body. The major functions of white adipocytes are to store energy as fat during periods when energy intake exceeds expenditure and to mobilize this stored fuel when energy expenditure exceeds intake. Brown/beige adipocytes contribute to non-shivering thermogenesis upon cold exposure and adrenergic stimulation, and thereby promote energy consumption. The imbalance of energy intake and expenditure causes obesity. Recent interest in epigenetics and signaling pathways has utilized small molecule tools aimed at modifying obesity-specific gene expression. In this review, we discuss compounds with adipogenesis-related signaling pathways and epigenetic modulating properties that have been identified as potential therapeutic agents which cast some light on the future treatment of obesity.

Ajuba functions as a co-activator of C/EBPβ to induce expression of PPARγ and C/EBPα during adipogenesis

Adipogenesis is regulated by a complicated network of transcription factors among which PPARγ and C/EBP family members are the major regulators. During adipogenesis, C/EBPβ is induced early and then transactivates PPARγ and C/EBPα, which cooperatively induce genes whose expressions give rise to the mature adipocyte phenotype. Identifying the factors that influence the expression and activity of C/EBPβ should provide additional insight into the mechanisms regulating adipogenesis. Here, we demonstrate that depletion of Ajuba in 3T3-L1 cells significantly decreases mRNA and protein levels of PPARγ and C/EBPα and impairs adipocyte differentiation, while overexpression increases expression of these genes and promotes adipocyte differentiation. Moreover, restoration of C/EBPα or PPARγ expression in Ajuba-deficient 3T3-L1 cells improves the impaired lipid accumulation. Mechanistically, Ajuba interacts with C/EBPβ and recruits CBP to facilitate the binding of C/EBPβ to the promoter of PPARγ and C/EBPα, resulting in increased H3 histone acetylation and target gene expression. Collectively, these data indicate that Ajuba functions as a co-activator of C/EBPβ, and may be an important therapeutic target for combating obesity-related diseases.

Transcriptional and epigenetic control of adipocyte remodeling during obesity

The rising prevalence of obesity over the past decades coincides with the rising awareness that a detailed understanding of both adipose tissue biology and obesity-associated remodeling is crucial for developing therapeutic and preventive strategies. Substantial progress has been made in identifying the signaling pathways and transcriptional networks that orchestrate alterations of adipocyte gene expression linked to diverse phenotypes. Owing to recent advances in epigenomics, we also gained a better appreciation for the fact that different environmental cues can epigenetically reprogram adipocyte fate and function, mainly by altering DNA methylation and histone modification patterns. Intriguingly, it appears that transcription factors and chromatin-modifying coregulator complexes are the key regulatory components that coordinate both signaling-induced transcriptional and epigenetic alterations in adipocytes. In this review, we summarize and discuss current molecular insights into how these alterations and the involved regulatory components trigger adipogenesis and adipose tissue remodeling in response to energy surplus.

Artemisia scoparia promotes adipogenesis in the absence of adipogenic effectors

OBJECTIVE

Extracts of Artemisia scoparia (SCO) have antidiabetic properties in mice and enhance adipogenesis in vitro, but the underlying mechanisms are unknown. Thiazolidinediones, including rosiglitazone (ROSI), are pharmacological activators of peroxisome proliferator-activated receptor gamma that also promote adipogenesis. The aim of this study was to examine adipogenic pathways responsible for SCO-mediated adipogenesis and identify potential differences between SCO and ROSI in the ability to promote adipocyte development.

METHODS

The ability of SCO or ROSI to promote adipogenesis in 3T3-L1 cells following systematic omission of the common triad of adipogenic effectors dexamethasone, 1-methyl-3-isobutylxanthine (MIX), and insulin was examined. Adipogenesis was assessed by both neutral lipid quantitation and adipocyte marker gene expression.

RESULTS

The results demonstrate that SCO and ROSI promote adipogenesis and increase the expression of several peroxisome proliferator-activated receptor gamma target genes involved in lipid accumulation in the absence of MIX. However, ROSI can enhance adipogenesis in the absence of MIX and insulin and differentially regulates adipogenic and lipid metabolism genes as compared with SCO.

CONCLUSIONS

These data demonstrate the adipogenic capabilities of SCO are similar but not identical to ROSI, thereby warranting further research into SCO as a promising source of therapeutic compounds in the treatment of metabolic disease states.

Downregulation of SUV39H1 and CITED2 Exerts Additive Effect on Promoting Adipogenic Commitment of Human Mesenchymal Stem Cells

Human adipogenesis is the process through which uncommitted human mesenchymal stem cells (hMSCs) differentiate into adipocytes. Through a siRNA-based high-throughput screen that identifies adipogenic regulators whose expression knockdown leads to enhanced adipogenic differentiation of hMSCs, two new regulators, SUV39H1, a histone methyltransferase that catalyzes H3K9Me3, and CITED2, a CBP/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 were uncovered. Both SUV39H1 and CITED2 are normally downregulated during adipogenic differentiation of hMSCs. Further expression knockdown induced by siSUV39H1 or siCITED2 at the adipogenic initiation stage significantly enhanced adipogenic differentiation of hMSCs as compared with siControl treatment, with siSUV39H1 acting by both accelerating fat accumulation in individual adipocytes and increasing the total number of committed adipocytes, whereas siCITED2 acting predominantly by increasing the total number of committed adipocytes. In addition, both siSUV39H1 and siCITED2 were able to redirect hMSCs to undergo adipogenic differentiation in the presence of osteogenic inducing media, which normally only induces osteogenic differentiation of hMSCs in the absence of siSUV39H1 or siCITED2. Interestingly, simultaneous knockdown of both SUV39H1 and CITED2 resulted in even greater levels of adipogenic differentiation of hMSCs and expression of CEBPα and PPARγ, two master regulators of adipogenesis, as compared with those elicited by single gene knockdown. Furthermore, the effects of co-knockdown were equivalent to the additive effect of individual gene knockdown. Taken together, this study demonstrates that SUV39H1 and CITED2 are both negative regulators of human adipogenesis, and downregulation of both genes exerts an additive effect on promoting adipogenic differentiation of hMSCs through augmented commitment.

Epigenetic Regulators of White Adipocyte Browning

Adipocytes play an essential role in maintaining energy homeostasis in mammals. The primary function of white adipose tissue (WAT) is to store energy; for brown adipose tissue (BAT), primary function is to release fats in the form of heat. Dysfunctional or excess WAT can induce metabolic disorders such as dyslipidemia, obesity, and diabetes. Preadipocytes or adipocytes from WAT possess sufficient plasticity as they can transdifferentiate into brown-like beige adipocytes. Studies in both humans and rodents showed that brown and beige adipocytes could improve metabolic health and protect from metabolic disorders. Brown fat requires activation via exposure to cold or β-adrenergic receptor (β-AR) agonists to protect from hypothermia. Considering the fact that the usage of β-AR agonists is still in question with their associated side effects, selective induction of WAT browning is therapeutically important instead of activating of BAT. Hence, a better understanding of the molecular mechanisms governing white adipocyte browning is vital. At the same time, it is also essential to understand the factors that define white adipocyte identity and inhibit white adipocyte browning. This literature review is a comprehensive and focused update on the epigenetic regulators crucial for differentiation and browning of white adipocytes.

Adipogenesis: A Complex Interplay of Multiple Molecular Determinants and Pathways

The formation of adipocytes during embryogenesis has been largely understudied. However, preadipocytes appear to originate from multipotent mesenchymal stromal/stem cells which migrate from the mesoderm to their anatomical localization. Most studies on adipocyte formation (adipogenesis) have used preadipocytes derived from adult stem/stromal cells. Adipogenesis consists of two phases, namely commitment and terminal differentiation. This review discusses the role of signalling pathways, epigenetic modifiers, and transcription factors in preadipocyte commitment and differentiation into mature adipocytes, as well as limitations in our understanding of these processes. To date, a limited number of transcription factors, genes and signalling pathways have been described to regulate preadipocyte commitment. One reason could be that most studies on adipogenesis have used preadipocytes already committed to the adipogenic lineage, which are therefore not suitable for studying preadipocyte commitment. Conversely, over a dozen molecular players including transcription factors, genes, signalling pathways, epigenetic regulators, and microRNAs have been described to be involved in the differentiation of preadipocytes to adipocytes; however, only peroxisome proliferator-activated receptor gamma has proven to be clinically relevant. A detailed understanding of how the molecular players underpinning adipogenesis relate to adipose tissue function could provide new therapeutic approaches for addressing obesity without compromising adipose tissue function.

AFF1 inhibits adipogenic differentiation via targeting TGM2 transcription

OBJECTIVES

AF4/FMR2 family member 1 (AFF1), known as a central scaffolding protein of super elongation complex (SEC), regulates gene transcription. We previously reported that AFF1 inhibited osteogenic differentiation of human mesenchymal stromal/stem cells (hMSCs). However, its role in adipogenic differentiation has not been elucidated.

MATERIALS AND METHODS

hMSCs and 3T3-L1 pre-adipocytes were cultured and induced for adipogenic differentiation. Small interfering RNAs (siRNAs) were applied to deplete AFF1 while lentiviruses expressing HA-Aff1 were used for overexpression. Oil Red O staining, triglyceride (TAG) quantification, quantitative real-time PCR (qPCR), Western blot analysis, immunofluorescence staining, RNA sequencing (RNA-seq) analysis and ChIP-qPCR were performed. To evaluate the adipogenesis in vivo, BALB/c nude mice were subcutaneously injected with Aff1-overexpressed 3T3-L1 pre-adipocytes.

RESULTS

AFF1 depletion leads to an enhanced adipogenesis in both hMSCs and 3T3-L1 pre-adipocytes. Overexpression of Aff1 in 3T3-L1 cells results in the reduction of adipogenic differentiation and less adipose tissue formation in vivo. Mechanistically, AFF1 binds to the promoter region of Tgm2 gene and regulates its transcription. Overexpression of Tgm2 largely rescues adipogenic differentiation of Aff1-deficient cells.

CONCLUSIONS

Our data indicate that AFF1 inhibits adipogenic differentiation by regulating the transcription of TGM2.

Control of mesenchymal stem cell biology by histone modifications

Mesenchymal stem cells (MSCs) are considered the most promising seed cells for regenerative medicine because of their considerable therapeutic properties and accessibility. Fine-tuning of cell biological processes, including differentiation and senescence, is essential for achievement of the expected regenerative efficacy. Researchers have recently made great advances in understanding the spatiotemporal gene expression dynamics that occur during osteogenic, adipogenic and chondrogenic differentiation of MSCs and the intrinsic and environmental factors that affect these processes. In this context, histone modifications have been intensively studied in recent years and have already been indicated to play significant and universal roles in MSC fate determination and differentiation. In this review, we summarize recent discoveries regarding the effects of histone modifications on MSC biology. Moreover, we also provide our insights and perspectives for future applications.

Regulation of Thermogenic Adipocyte Differentiation and Adaptive Thermogenesis Through Histone Acetylation

Over the past decade, the increasing prevalence of obesity and its associated metabolic disorders constitutes one of the most concerning healthcare issues for countries worldwide. In an effort to curb the increased mortality and morbidity derived from the obesity epidemic, various therapeutic strategies have been developed by researchers. In the recent years, advances in the field of adipocyte biology have revealed that the thermogenic adipose tissue holds great potential in ameliorating metabolic disorders. Additionally, epigenetic research has shed light on the effects of histone acetylation on adipogenesis and thermogenesis, thereby establishing the essential roles which histone acetyltransferases (HATs) and histone deacetylases (HDACs) play in metabolism and systemic energy homeostasis. In regard to the therapeutic potential of thermogenic adipocytes for the treatment of metabolic diseases, herein, we describe the current state of knowledge of the regulation of thermogenic adipocyte differentiation and adaptive thermogenesis through histone acetylation. Furthermore, we highlight how different HATs and HDACs maintain the epigenetic transcriptional network to mediate the pathogenesis of various metabolic comorbidities. Finally, we provide insights into recent advances of the potential therapeutic applications and development of HAT and HDAC inhibitors to alleviate these pathological conditions.

Transcriptional and Epigenomic Regulation of Adipogenesis

Understanding adipogenesis, the process of adipocyte development, may provide new ways to treat obesity and related metabolic diseases. Adipogenesis is controlled by coordinated actions of lineage-determining transcription factors and epigenomic regulators. Peroxisome proliferator-activated receptor gamma (PPARγ) and C/EBPα are master "adipogenic" transcription factors. In recent years, a growing number of studies have reported the identification of novel transcriptional and epigenomic regulators of adipogenesis. However, many of these novel regulators have not been validated in adipocyte development in vivo and their working mechanisms are often far from clear. In this minireview, we discuss recent advances in transcriptional and epigenomic regulation of adipogenesis, with a focus on factors and mechanisms shared by both white adipogenesis and brown adipogenesis. Studies on the transcriptional regulation of adipogenesis highlight the importance of investigating adipocyte differentiation in vivo rather than drawing conclusions based on knockdown experiments in cell culture. Advances in understanding of epigenomic regulation of adipogenesis have revealed critical roles of histone methylation/demethylation, histone acetylation/deacetylation, chromatin remodeling, DNA methylation, and microRNAs in adipocyte differentiation. We also discuss future research directions that may help identify novel factors and mechanisms regulating adipogenesis.

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

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

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

Urate transporter inhibitor lesinurad is a selective peroxisome proliferator-activated receptor gamma modulator (sPPARγM) in vitro

Gout is the most common arthritic disease in human but was long neglected and therapeutic options are not satisfying. However, with the recent approval of the urate transporter inhibitor lesinurad, gout treatment has experienced a major innovation. Here we show that lesinurad possesses considerable modulatory potency on peroxisome proliferator-activated receptor γ (PPARγ). Since gout has a strong association with metabolic diseases such as type 2 diabetes, this side-activity appears as very valuable contributing factor to the clinical efficacy profile of lesinurad. Importantly, despite robustly activating PPARγ in vitro, lesinurad lacked adipogenic activity, which seems due to differential coactivator recruitment and is characterized as selective PPARγ modulator (sPPARγM).

Lanthionine synthetase C-like protein 2 (LanCL2) is important for adipogenic differentiation

Adipogenic differentiation is a highly regulated process that is necessary for metabolic homeostasis and nutrient sensing. The expression of PPARγ and the subsequent activation of adipogenic genes is critical for the process. In this study, we identified lanthionine synthetase C-like protein 2 (LanCL2) as a positive regulator of adipogenesis in 3T3-L1 cells. Knockdown of LanCL2, but not LanCL1, inhibited adipogenic differentiation, and this effect was not mediated through cAMP or Akt signaling pathways. The expression of early adipogenic markers CCAAT enhancer binding protein β (C/EBPβ) and C/EBPδ remained intact in LanCL2 knockdown cells, but levels of late adipogenic markers PPARγ and C/EBPα were suppressed. The addition of the naturally occurring PPARγ activator 15-deoxy-Δ^12,14-prostaglandin J2 or conditioned medium from differentiating cells did not restore differentiation, implying that LanCL2 may not be involved in the production of a secreted endogenous PPARγ ligand. Pulldown assays demonstrated a direct physical interaction between LanCL2 and PPARγ. Consistent with a regulatory role of LanCL2, luciferase reporter assays revealed that full transcriptional activation by PPARγ was dependent on LanCL2. Taken together, our study reveals a novel role of LanCL2 in adipogenesis, specifically involved in PPARγ-mediated transactivation of downstream adipogenic genes.

Ginkgolic acid, a sumoylation inhibitor, promotes adipocyte commitment but suppresses adipocyte terminal differentiation of mouse bone marrow stromal cells

Sumoylation is a post-translational modification process having an important influence in mesenchymal stem cell (MSC) differentiation. Thus, sumoylation-modulating chemicals might be used to control MSC differentiation for skeletal tissue engineering. In this work, we studied how the differentiation of mouse bone marrow stromal cells (mBMSCs) is affected by ginkgolic acid (GA), a potent sumoylation inhibitor also reported to inhibit histone acetylation transferase (HAT). Our results show that GA promoted the differentiation of mBMSCs into adipocytes when cultured in osteogenic medium. Moreover, mBMSCs pre-treated with GA showed enhanced pre-adipogenic gene expression and were more efficiently differentiated into adipocytes when subsequently cultured in the adipogenic medium. However, when GA was added at a later stage of adipogenesis, adipocyte maturation was markedly inhibited, with a dramatic down-regulation of multiple lipogenesis genes. Moreover, we found that the effects of garcinol, a HAT inhibitor, differed from those of GA in regulating adipocyte commitment and adipocyte maturation of mBMSCs, implying that the GA function in adipogenesis is likely through its activity as a sumoylation inhibitor, not as a HAT inhibitor. Overall, our studies revealed an unprecedented role of GA in MSC differentiation and provide new mechanistic insights into the use of GA in clinical applications.

Deciphering the Roles of PPARγ in Adipocytes via Dynamic Change of Transcription Complex

Peroxisome proliferator-activated receptor γ (PPARγ), a ligand-dependent transcription factor highly expressed in adipocytes, is a master regulator of adipogenesis and lipid storage, a central player in thermogenesis and an active modulator of lipid metabolism and insulin sensitivity. As a nuclear receptor governing numerous target genes, its specific signaling transduction relies on elegant transcriptional and post-translational regulations. Notably, in response to different metabolic stimuli, PPARγ recruits various cofactors and forms distinct transcriptional complexes that change dynamically in components and epigenetic modification to ensure specific signal transduction. Clinically, PPARγ activation via its full agonists, thiazolidinediones, has been shown to improve insulin sensitivity and induce browning of white fat, while undesirably induce weight gain, visceral obesity and other adverse effects. Thus, deciphering the combinatorial interactions between PPARγ and its transcriptional partners and their preferential regulatory network in the processes of development, function and senescence of adipocytes would provide us the molecular basis for developing novel partial agonists that promote benefits of PPARγ signaling without detrimental side effects. In this review, we discuss the dynamic components and precise regulatory mechanisms of the PPARγ-cofactors complexes in adipocytes, as well as perspectives in treating metabolic diseases via specific PPARγ signaling.

MLL3/MLL4 are required for CBP/p300 binding on enhancers and super-enhancer formation in brown adipogenesis

Histone H3K4me1/2 methyltransferases MLL3/MLL4 and H3K27 acetyltransferases CBP/p300 are major enhancer epigenomic writers. To understand how these epigenomic writers orchestrate enhancer landscapes in cell differentiation, we have profiled genomic binding of MLL4, CBP, lineage-determining transcription factors (EBF2, C/EBPβ, C/EBPα, PPARγ), coactivator MED1, RNA polymerase II, as well as epigenome (H3K4me1/2/3, H3K9me2, H3K27me3, H3K36me3, H3K27ac), transcriptome and chromatin opening during adipogenesis of immortalized preadipocytes derived from mouse brown adipose tissue (BAT). We show that MLL4 and CBP drive the dynamic enhancer epigenome, which correlates with the dynamic transcriptome. MLL3/MLL4 are required for CBP/p300 binding on enhancers activated during adipogenesis. Further, MLL4 and CBP identify super-enhancers (SEs) of adipogenesis and that MLL3/MLL4 are required for SE formation. Finally, in brown adipocytes differentiated in culture, MLL4 identifies primed SEs of genes fully activated in BAT such as Ucp1. Comparison of MLL4-defined SEs in brown and white adipogenesis identifies brown-specific SE-associated genes that could be involved in BAT functions. These results establish MLL3/MLL4 and CBP/p300 as master enhancer epigenomic writers and suggest that enhancer-priming by MLL3/MLL4 followed by enhancer-activation by CBP/p300 sequentially shape dynamic enhancer landscapes during cell differentiation. Our data also provide a rich resource for understanding epigenomic regulation of brown adipogenesis.

Almond Skin Polyphenol Extract Inhibits Inflammation and Promotes Lipolysis in Differentiated 3T3-L1 Adipocytes

Studies have shown that polyphenols reduce the risk of inflammation-related diseases and upregulates energy expenditure in adipose tissue. Here, we investigated the mechanism of the anti-inflammatory and antiobesity effects of almond skin polyphenol extract (ASP) in differentiated 3T3-L1 adipocytes. The antioxidant effects of ASP were measured based on DPPH radical scavenging activity, Trolox equivalent antioxidant capacity, and total phenolic content. Differentiated 3T3-L1 cells were treated with ASP. Subsequently, lipolysis proteins and transcription factors of adipogenesis were measured. The proinflammatory mediators monocyte chemotactic protein-1 (MCP-1) and chemokine ligand 5 (CCL-5) were determined by enzyme-linked immunosorbent assay. We found that ASP significantly promoted phosphorylation of AMP-activated protein kinase (AMPK), increased activity of adipose triglyceride lipase and hormone-sensitive lipase, and inhibited adipogenesis-related transcription factors. In addition, ASP inhibited the tumor necrosis factor-α (TNF-α)-induced cell inflammatory response via downregulation of MCP-1 and CCL-5 secretion. This study suggests that ASP regulates lipolysis through activation of AMPK, reduced adipogenesis, and suppresses proinflammatory cytokines in adipocytes.

Remodeling of rat stromal-vascular cells to brite/beige adipocytes by prolyl-hydroxyproline

The aim of this study was to determine the effects of prolyl-hydroxyproline (Pro-Hyp) on the proliferation and differentiation of rat stromal-vascular cells (SVCs) being cultured in a medium with (Pro-Hyp group) or without Pro-Hyp (control group). The results showed that there was no significant difference in proliferation rate of SVCs, lipid droplet (LD) diameter or intracellular concentration of triglycerides between two groups. However, the diameter range of LDs in the Pro-Hyp group tended to be smaller than that in the control group. Transmission electron microscopy showed a tendency for increase in the area of mitochondria and decrease in the number of mitochondria in the Pro-Hyp-treated SVCs. The mRNA expression levels of white adipose tissue differentiation markers (Cbp, Fabp and Serpina3k) were significantly lower, but those of the brown adipose tissue differentiation markers (Dio2, Ucp1 and Ucp3) were significantly higher in the Pro-Hyp group than in the control group. Our results suggested that Pro-Hyp can facilitate SVCs to differentiate into “brite/beige” adipocytes.

Protein acetylation in metabolism - metabolites and cofactors

Reversible acetylation was initially described as an epigenetic mechanism regulating DNA accessibility. Since then, this process has emerged as a controller of histone and nonhistone acetylation that integrates key physiological processes such as metabolism, circadian rhythm and cell cycle, along with gene regulation in various organisms. The widespread and reversible nature of acetylation also revitalized interest in the mechanisms that regulate lysine acetyltransferases (KATs) and deacetylases (KDACs) in health and disease. Changes in protein or histone acetylation are especially relevant for many common diseases including obesity, diabetes mellitus, neurodegenerative diseases and cancer, as well as for some rare diseases such as mitochondrial diseases and lipodystrophies. In this Review, we examine the role of reversible acetylation in metabolic control and how changes in levels of metabolites or cofactors, including nicotinamide adenine dinucleotide, nicotinamide, coenzyme A, acetyl coenzyme A, zinc and butyrate and/or β-hydroxybutyrate, directly alter KAT or KDAC activity to link energy status to adaptive cellular and organismal homeostasis.

Histone H3 K27 acetylation marks a potent enhancer element on the adipogenic master regulator gene Pparg2

PPARγ2 is expressed almost exclusively in adipose tissue and plays a central role in adipogenesis. Despite intensive studies over the last 2 decades, the mechanism regulating the expression of the Pparg2 gene, especially the role of cis-regulatory elements, is still not completely understood. Here, we report a comprehensive investigation of the enhancer elements within the murine Pparg2 gene. Utilizing the combined techniques of sequence conservation analysis and chromatin marker examination, we identified a potent enhancer element that augmented the expression of a reporter gene under the control of the Pparg2 promoter by 20-fold. This enhancer element was first identified as highly conserved non-coding sequence 10 (CNS10) and was later shown to be enriched with the enhancer marker H3 K27 acetylation. Further studies identified a binding site for p300 as the essential enhancer element in CNS10. Moreover, p300 physically binds to CNS10 and is required for the enhancer activity of CNS10. The depletion of p300 by siRNA resulted in significantly impaired activation of Pparg2 at the early stages of 3T3-L1 adipogenesis. In summary, our study identified a novel enhancer element on the murine Pparg2 gene and suggested a novel mechanism for the regulation of Pparg2 expression by p300 in 3T3-L1 adipogenesis.

2,4,6-Trihydroxybenzaldehyde, a potential anti-obesity treatment, suppressed adipocyte differentiation in 3T3-L1 cells and fat accumulation induced by high-fat diet in C57BL/6 mice

In the present study, 2,4,6-trihydroxybenzaldehyde (THB) was evaluated for inhibitory effects on adipocyte differentiation in 3T3-L1 cells and anti-obesity effects in mice with high-fat diet (HFD)-induced obesity. Lipid accumulation measurement indicated that THB markedly inhibited adipogenesis, and this involved down-regulation of the expression of the adipogenesis-related proteins, CCAAT/enhancer-binding protein α (C/EBPα), peroxisome proliferator-activated receptor γ (PPARγ), fatty acid synthase (FAS) and sterol regulatory element-binding protein-1c (SREBP-1c), in 3T3-L1 pre-adipocyte cells. In a mouse model of HFD-induced obesity, oral administration of THB (5 and 25mg/kg for 13 weeks) reduced the HFD-induced increase in weight gain. THB administration also reduced serum levels of glucose, triglycerides, and total cholesterol. A reduction in the hypertrophy of white adipose tissue was also observed. Furthermore, THB administration inhibited HFD-induced hepatic steatosis. These results provided evidence that administration of THB alleviated HFD-induced obesity in C57BL/6 mice and revealed the potential of THB as a nutraceutical to help prevent or treat obesity and the associated metabolic disorders.

Activation of peroxisome proliferator-activated receptor-α (PPARα) in proximal intestine improves postprandial lipidemia in obese diabetic KK-Ay mice

Postprandial lipidemia is a risk factor for cardiovascular diseases. Thus, the suppression of postprandial lipidemia is valuable for disease management. Peroxisome proliferator-activated receptor- (PPAR ) is a key regulator in the lipid metabolism of peripheral tissues such as the liver and skeletal muscle, whose activation enhances fatty acid oxidation and decreases circulating lipid level. Recently, we have shown that bezafibrate, an agonistic compound for PPAR , suppresses post-prandial lipidemia by enhancing fatty acid oxidation in intestinal epithelial cells under physiological conditions. However, it was not elucidated whether the effect of PPAR on postprandial lipidemia is also observed under obese conditions, which change lipid metabolisms in various tissues and cells. Here, we observed that bezafibrate enhanced fatty acid oxidation in intestinal epithelial cells of obese diabetic KK-Ay mice. Bezafibrate treatment increased the mRNA expression levels of fatty acid oxidation-related genes, which are targets of PPAR , and enhanced CO2 production from [14C]-palmitic acid. The bezafibrate-treated mice showed the suppression of increasing serum triacylglyceride level after the oral administration of olive oil. Moreover, the effects of bezafibrate on mRNA expression and fatty acid oxidation were shown in only the proximal intestinal epithelial cells. These findings indicate that PPAR activation suppresses postprandial lipidemia under obese conditions through the enhancement of fatty acid oxidation, and that only the proximal intestine con-tributes to the effects in mice, suggesting that intestinal PPAR can be a target for prevention of obese-induced postprandial lipidemia.

Gcn5 and PCAF regulate PPARγ and Prdm16 expression to facilitate brown adipogenesis

The acetyltransferase Gcn5 is critical for embryogenesis and shows partial functional redundancy with its homolog PCAF. However, the tissue- and cell lineage-specific functions of Gcn5 and PCAF are still not well defined. Here we probe the functions of Gcn5 and PCAF in adipogenesis. We found that the double knockout (DKO) of Gcn5/PCAF inhibits expression of the master adipogenic transcription factor gene PPARγ, thereby preventing adipocyte differentiation. The adipogenesis defects in Gcn5/PCAF DKO cells are rescued by ectopic expression of peroxisome proliferator-activated receptor γ (PPARγ), suggesting Gcn5/PCAF act upstream of PPARγ to facilitate adipogenesis. The requirement of Gcn5/PCAF for PPARγ expression was unexpectedly bypassed by prolonged treatment with an adipogenic inducer, 3-isobutyl-1-methylxanthine (IBMX). However, neither PPARγ ectopic expression nor prolonged IBMX treatment rescued defects in Prdm16 expression in DKO cells, indicating that Gcn5/PCAF are essential for normal Prdm16 expression. Gcn5/PCAF regulate PPARγ and Prdm16 expression at different steps in the transcription process, facilitating RNA polymerase II recruitment to Prdm16 and elongation of PPARγ transcripts. Overall, our study reveals that Gcn5/PCAF facilitate adipogenesis through regulation of PPARγ expression and regulate brown adipogenesis by influencing Prdm16 expression.

Yamogenin in fenugreek inhibits lipid accumulation through the suppression of gene expression in fatty acid synthesis in hepatocytes

Yamogenin is a diastereomer of diosgenin, which we have identified as the compound responsible for the anti-hyperlipidemic effect of fenugreek. Here, we examined the effects of yamogenin on the accumulation of triacylglyceride (TG) in hepatocytes, because yamogenin is also contained in fenugreek. It was demonstrated that yamogenin also inhibited TG accumulation in HepG2 hepatocytes and suppressed the mRNA expression of fatty acid synthesis-related genes such as fatty acid synthase and sterol response element-binding protein-1c. Indeed, yamogenin also antagonized the activation of the liver X receptor (LXR) in luciferase ligand assay similar to diosgenin. However, yamogenin could not exert such effects in the presence of T0901713, a potent agonist of LXR. These findings indicate that the effects of yamogenin on TG accumulation would be weaker than those of diosgenin, suggesting that the structural difference between yamogenin and diosgenin would be important for the inhibition of LXR activation.

Transcriptional and epigenetic regulation of PPARγ expression during adipogenesis

The nuclear receptor PPARγ is a master regulator of adipogenesis. PPARγ is highly expressed in adipose tissues and its expression is markedly induced during adipogenesis. In this review, we describe the current knowledge, as well as future directions, on transcriptional and epigenetic regulation of PPARγ expression during adipogenesis. Investigating the molecular mechanisms that control PPARγ expression during adipogenesis is critical for understanding the development of white and brown adipose tissues, as well as pathological conditions such as obesity and diabetes. The robust induction of PPARγ expression during adipogenesis also serves as an excellent model system for studying transcriptional and epigenetic regulation of cell-type-specific gene expression.

From SNP co-association to RNA co-expression: novel insights into gene networks for intramuscular fatty acid composition in porcine

Background

Fatty acids (FA) play a critical role in energy homeostasis and metabolic diseases; in the context of livestock species, their profile also impacts on meat quality for healthy human consumption. Molecular pathways controlling lipid metabolism are highly interconnected and are not fully understood. Elucidating these molecular processes will aid technological development towards improvement of pork meat quality and increased knowledge of FA metabolism, underpinning metabolic diseases in humans.

Results

The results from genome-wide association studies (GWAS) across 15 phenotypes were subjected to an Association Weight Matrix (AWM) approach to predict a network of 1,096 genes related to intramuscular FA composition in pigs. To identify the key regulators of FA metabolism, we focused on the minimal set of transcription factors (TF) that the explored the majority of the network topology. Pathway and network analyses pointed towards a trio of TF as key regulators of FA metabolism: NCOA2, FHL2 and EP300. Promoter sequence analyses confirmed that these TF have binding sites for some well-know regulators of lipid and carbohydrate metabolism. For the first time in a non-model species, some of the co-associations observed at the genetic level were validated through co-expression at the transcriptomic level based on real-time PCR of 40 genes in adipose tissue, and a further 55 genes in liver. In particular, liver expression of NCOA2 and EP300 differed between pig breeds (Iberian and Landrace) extreme in terms of fat deposition. Highly clustered co-expression networks in both liver and adipose tissues were observed. EP300 and NCOA2 showed centrality parameters above average in the both networks. Over all genes, co-expression analyses confirmed 28.9% of the AWM predicted gene-gene interactions in liver and 33.0% in adipose tissue. The magnitude of this validation varied across genes, with up to 60.8% of the connections of NCOA2 in adipose tissue being validated via co-expression.

Conclusions

Our results recapitulate the known transcriptional regulation of FA metabolism, predict gene interactions that can be experimentally validated, and suggest that genetic variants mapped to EP300, FHL2, and NCOA2 modulate lipid metabolism and control energy homeostasis in pigs.

Role of histone acetyltransferases and histone deacetylases in adipocyte differentiation and adipogenesis

Adipogenesis is a complex process strictly regulated by a well-established cascade that has been thoroughly studied in the last two decades. This process is governed by complex regulatory networks that involve the activation/inhibition of multiple functional genes, and is controlled by histone-modifying enzymes. Among such modification enzymes, histone acetyltransferases (HATs) and histone deacetylases (HDACs) play important roles in the transcriptional regulation and post-translational modification of protein acetylation. HATs and HDACs have been shown to respond to signals that regulate cell differentiation, participate in the regulation of protein acetylation, mediate transcription and post-translation modifications, and directly acetylate/deacetylate various transcription factors and regulatory proteins. In this paper, we review the role of HATs and HDACs in white and brown adipocyte differentiation and adipogenesis, to expand our knowledge on fat formation and adipose tissue biology.

LT175 is a novel PPARα/γ ligand with potent insulin-sensitizing effects and reduced adipogenic properties

Peroxisome proliferator-activated receptors (PPARs) are ligand-dependent transcription factors regulating lipid and glucose metabolism. Ongoing drug discovery programs aim to develop dual PPARα/γ agonists devoid of the side effects of the marketed antidiabetic agents thiazolidinediones and the dual agonists glitazars. Recently, we described a new dual PPARα/γ ligand, LT175, with a partial agonist profile against PPARγ and interacting with a newly identified region of the PPARγ-ligand binding domain (1). Here we show that LT175 differentially activated PPARγ target genes involved in fatty acid esterification and storage in 3T3-L1-derived adipocytes. This resulted in a less severe lipid accumulation compared with that triggered by rosiglitazone, suggesting that LT175 may have a lower adipogenic activity. Consistent with this hypothesis, in vivo administration of LT175 to mice fed a high-fat diet decreased body weight, adipocyte size, and white adipose tissue mass, as assessed by magnetic resonance imaging. Furthermore, LT175 significantly reduced plasma glucose, insulin, non-esterified fatty acids, triglycerides, and cholesterol and increased circulating adiponectin and fibroblast growth factor 21 levels. Oral glucose and insulin tolerance tests showed that the compound improves glucose homeostasis and insulin sensitivity. Moreover, we demonstrate that the peculiar interaction of LT175 with PPARγ affected the recruitment of the coregulators cyclic-AMP response element-binding protein-binding protein and nuclear corepressor 1 (NCoR1), fundamentals for the PPARγ-mediated adipogenic program. In conclusion, our results describe a new PPAR ligand, modulating lipid and glucose metabolism with reduced adipogenic activity, that may be used as a model for a series of novel molecules with an improved pharmacological profile for the treatment of dyslipidemia and type 2 diabetes.

Metabolic mystery: aging, obesity, diabetes, and the ventromedial hypothalamus

We propose that energy balance, glucose homeostasis, and aging are all regulated largely by the same nutrient-sensing neurons in the ventromedial hypothalamus (VMH). Although the central role of these neurons in regulating energy balance is clear, their role in regulating glucose homeostasis has only recently become more clear. This latter function may be most relevant to aging and lifespan by controlling the rate of glucose metabolism. Specifically, glucose-sensing neurons in VMH promote peripheral glucose metabolism, and dietary restriction, by reducing glucose metabolism in these neurons, reduces glucose metabolism of the rest of the body, thereby increasing lifespan. Here we discuss recent studies demonstrating the key role of hypothalamic neurons in driving aging and age-related diseases.

Modulation of the transcriptional activity of peroxisome proliferator-activated receptor gamma by protein-protein interactions and post-translational modifications

Peroxisome proliferator-activated receptor gamma (PPARγ) belongs to a nuclear receptor superfamily; members of which play key roles in the control of body metabolism principally by acting on adipose tissue. Ligands of PPARγ, such as thiazolidinediones, are widely used in the treatment of metabolic syndromes and type 2 diabetes mellitus (T2DM). Although these drugs have potential benefits in the treatment of T2DM, they also cause unwanted side effects. Thus, understanding the molecular mechanisms governing the transcriptional activity of PPARγ is of prime importance in the development of new selective drugs or drugs with fewer side effects. Recent advancements in molecular biology have made it possible to obtain a deeper understanding of the role of PPARγ in body homeostasis. The transcriptional activity of PPARγ is subject to regulation either by interacting proteins or by modification of the protein itself. New interacting partners of PPARγ with new functions are being unveiled. In addition, post-translational modification by various cellular signals contributes to fine-tuning of the transcriptional activities of PPARγ. In this review, we will summarize recent advancements in our understanding of the post-translational modifications of, and proteins interacting with, PPARγ, both of which affect its transcriptional activities in relation to adipogenesis.

Role of the hypothalamus in mediating protective effects of dietary restriction during aging

Dietary restriction (DR) can extend lifespan and reduce disease burden across a wide range of animals and yeast but the mechanisms mediating these remarkably protective effects remain to be elucidated despite extensive efforts. Although it has generally been assumed that protective effects of DR are cell-autonomous, there is considerable evidence that many whole-body responses to nutritional state, including DR, are regulated by nutrient-sensing neurons. In this review, we explore the hypothesis that nutrient sensing neurons in the ventromedial hypothalamus hierarchically regulate the protective responses of dietary restriction. We describe multiple peripheral responses that are hierarchically regulated by the hypothalamus and we present evidence for non-cell autonomous signaling of dietary restriction gathered from a diverse range of models including invertebrates, mammalian cell culture, and rodent studies.

THRAP3 interacts with HELZ2 and plays a novel role in adipocyte differentiation

Using yeast two-hybrid screen, we previously isolated HELZ2 (helicase with zinc finger 2, transcriptional coactivator) that functions as a coregulator of peroxisome proliferator-activated receptorγ (PPARγ). To further delineate its molecular function, we here identified thyroid hormone receptor-associated protein3 (THRAP3), a putative component of the Mediator complex, as a protein stably associating with HELZ2 using immunoprecipitation coupled with mass spectrometry analyses. In immunoprecipitation assays, Thrap3 could associate with endogenous Helz2 as well as Pparg in differentiated 3T3-L1 cells. HELZ2 interacts with the serine/arginine-rich domain and Bcl2 associated transcription factor1-homologous region in THRAP3, whereas THRAP3 directly binds 2 helicase motifs in HELZ2. HELZ2 and THRAP3 synergistically augment transcriptional activation mediated by PPARγ, whereas knockdown of endogenous THRAP3 abolished the enhancement by HELZ2 in reporter assays. Thrap3, similar to Helz2, is evenly expressed in the process of adipogenic differentiation in 3T3-L1 cells. Knockdown of Thrap3 in 3T3-L1 preadipocytes using short-interfering RNA did not influence the expression of Krox20, Klf5, Cebpb, or Cebpd during early stages of adipocyte differentiation, but significantly attenuated the expression of Pparg, Cebpa, and Fabp4/aP2 and accumulation of lipid droplets. Pharmacologic activation of Pparg by troglitazone could not fully restore the differentiation of Thrap3-knockdown adipocytes. In chromatin immunoprecipitation assays, endogenous Helz2 and Thrap3 could be co-recruited, in a ligand-dependent manner, to the PPARγ-response elements in Fabp4/aP2 and Adipoq gene enhancers in differentiated 3T3-L1 cells. These findings collectively suggest that Thrap3 could play indispensable roles in terminal differentiation of adipocytes by enhancing PPARγ-mediated gene activation cooperatively with Helz2.