Transcription coactivator TRAP220 is required for PPAR gamma 2-stimulated adipogenesis

Compromised Peroxisome Proliferator-Activated Receptor γ-Mediated Impaired Placental Glucose Transport Via the Phosphatidylinositol 3-Kinase/Protein Kinase B Signaling Pathway Is Associated With Fetal Growth Restriction

Fetal growth restriction (FGR) is a condition in which a fetus cannot grow to its full potential during pregnancy. It is a leading cause of perinatal mortality and morbidity. However, the underlying etiology remains elusive. Here, we report that peroxisome proliferator-activated receptor γ (PPARγ) is inactivated in the trophoblasts of the human placenta of FGR-complicated pregnancies. In the FGR placentas, p-PI3KTyr458 and p-AKTSer473 levels were also lowered. Additionally, there was a reduction in GLUT3 and GLUT4 levels in the cell membrane. Consistently, FGR patients showed decreased glucose concentrations in both the placenta and umbilical cord blood compared with that in normal pregnancy. In mouse models, deletion of Pparg in trophoblasts and reduced uterine perfusion pressure surgery successfully induced FGR and replicated these changes. Modulating PPARγ activity using rosiglitazone or GW9662 in BeWo cells, a model of syncytiotrophoblasts, resulted in the activation or inhibition of the phosphatidylinositol 3-kinase/protein kinase B signaling pathway, as well as the promotion or reduction of membrane translocation of GLUT3 and GLUT4, ultimately affecting glucose uptake in trophoblast cells. MK-2206 blocked these regulatory effects of rosiglitazone in BeWo cells. Furthermore, the administration of rosiglitazone encapsulated in placenta-targeting nanoparticles improved the growth and development of fetal mice in the reduced uterine perfusion pressure group. In summary, PPARγ in trophoblast cells orchestrates the translocation of GLUT3 and GLUT4 to the cellular membrane via the phosphatidylinositol 3-kinase/protein kinase B signaling pathway, thereby regulating cellular glucose uptake and transport. Dysfunctions in this mechanism are strongly associated with FGR. Therefore, targeted activation of PPARγ in the placenta may be a potentially efficacious intrauterine intervention for FGR.

Unanticipated mechanisms of covalent inhibitor and synthetic ligand cobinding to PPARγ

Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor transcription factor that regulates gene expression programs in response to ligand binding. Endogenous and synthetic ligands, including covalent antagonist inhibitors GW9662 and T0070907, are thought to compete for the orthosteric pocket in the ligand-binding domain (LBD). However, we previously showed that synthetic PPARγ ligands can cooperatively cobind with and reposition a bound endogenous orthosteric ligand to an alternate site, synergistically regulating PPARγ structure and function (Shang et al., 2018). Here, we reveal the structural mechanism of cobinding between a synthetic covalent antagonist inhibitor with other synthetic ligands. Biochemical and NMR data show that covalent inhibitors weaken-but do not prevent-the binding of other ligands via an allosteric mechanism, rather than direct ligand clashing, by shifting the LBD ensemble toward a transcriptionally repressive conformation, which structurally clashes with orthosteric ligand binding. Crystal structures reveal different cobinding mechanisms including alternate site binding to unexpectedly adopting an orthosteric binding mode by altering the covalent inhibitor binding pose. Our findings highlight the significant flexibility of the PPARγ orthosteric pocket, its ability to accommodate multiple ligands, and demonstrate that GW9662 and T0070907 should not be used as chemical tools to inhibit ligand binding to PPARγ.

Unanticipated mechanisms of covalent inhibitor and synthetic ligand cobinding to PPARγ

Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor transcription factor that regulates gene expression programs in response to ligand binding. Endogenous lipids and synthetic ligands, including covalent antagonist inhibitors such as GW9662 and T0070907, are thought to compete for the orthosteric pocket in the ligand-binding domain (LBD). However, we previously showed that synthetic PPARγ ligands can cooperatively cobind with and reposition a bound endogenous orthosteric ligand to an alternate site, synergistically regulating PPARγ structure and function (Shang et al., 2018). Here, we reveal the structural mechanism of cobinding between a synthetic covalent antagonist inhibitor with other synthetic ligands. Biochemical and NMR data show that covalent antagonist inhibitors weaken-but do not prevent-the binding of other synthetic ligands via an allosteric mechanism rather than direct ligand clashing. The covalent ligands shift the LBD ensemble toward a transcriptionally repressive conformation, which structurally clashes with and reduces the orthosteric binding affinity of non-covalent synthetic ligands. Crystal structures reveal different non-covalent synthetic ligand-specific cobinding mechanisms ranging from alternate site binding to unexpectedly adopting an orthosteric binding mode by altering the covalent ligand binding pose. Our findings not only highlight the significant flexibility of the PPARγ orthosteric pocket and its ability to accommodate multiple ligands simultaneously, but also demonstrate that GW9662 and T0070907 should not be used as reliable chemical tools to inhibit the binding of other ligands to PPARγ.

A Closer Look into White Adipose Tissue Biology and the Molecular Regulation of Stem Cell Commitment and Differentiation

White adipose tissue (WAT) makes up about 20-25% of total body mass in healthy individuals and is crucial for regulating various metabolic processes, including energy metabolism, endocrine function, immunity, and reproduction. In adipose tissue research, "adipogenesis" is commonly used to refer to the process of adipocyte formation, spanning from stem cell commitment to the development of mature, functional adipocytes. Although, this term should encompass a wide range of processes beyond commitment and differentiation, to also include other stages of adipose tissue development such as hypertrophy, hyperplasia, angiogenesis, macrophage infiltration, polarization, etc.… collectively, referred to herein as the adipogenic cycle. The term "differentiation", conversely, should only be used to refer to the process by which committed stem cells progress through distinct phases of subsequent differentiation. Recognizing this distinction is essential for accurately interpreting research findings on the mechanisms and stages of adipose tissue development and function. In this review, we focus on the molecular regulation of white adipose tissue development, from commitment to terminal differentiation, and examine key functional aspects of WAT that are crucial for normal physiology and systemic metabolic homeostasis.

TGS1/PIMT knockdown reduces lipid accumulation in adipocytes, limits body weight gain and promotes insulin sensitivity in mice

PRIP Interacting protein with Methyl Transferase domain (PIMT/TGS1) is an integral upstream coactivator in the peroxisome proliferator-activated receptor gamma (PPARγ) transcriptional apparatus. PPARγ activation alleviates insulin resistance but promotes weight gain. Herein, we show how PIMT regulates body weight while promoting insulin sensitivity in diet induced obese mice. In vitro, we observed enhanced PIMT levels during adipogenesis. Knockdown of PIMT in 3T3-L1 results in reduced lipid accumulation and alters PPARγ regulated gene expression. Intraperitoneal injection of shPIMT lentivirus in high fat diet (HFD)-fed mice caused reduced adipose tissue size and decreased expression of lipid markers. This was accompanied by significantly lower levels of inflammation, hypertrophy and hyperplasia in the different adipose depots (eWAT and iWAT). Notably, PIMT depletion limits body weight gain in HFD-fed mice along with improved impaired oral glucose clearance. It also enhanced insulin sensitivity revealed by assessment of important insulin resistance markers and increased adiponectin levels. In addition, reduced PIMT levels did not alter the serum free fatty acid and TNFα levels. Finally, the relevance of our studies to human obesity is suggested by our finding that PIMT was upregulated in adipose tissue of obese patients along with crucial fat marker genes. We speculate that PIMT may be a potential target in maintaining energy metabolism, thus regulating obesity.

Regulation of the RNA polymerase II pre-initiation complex by its associated coactivators

The RNA polymerase II (Pol II) pre-initiation complex (PIC) is a critical node in eukaryotic transcription regulation, and its formation is the major rate-limiting step in transcriptional activation. Diverse cellular signals borne by transcriptional activators converge on this large, multiprotein assembly and are transduced via intermediary factors termed coactivators. Cryogenic electron microscopy, multi-omics and single-molecule approaches have recently offered unprecedented insights into both the structure and cellular functions of the PIC and two key PIC-associated coactivators, Mediator and TFIID. Here, we review advances in our understanding of how Mediator and TFIID interact with activators and affect PIC formation and function. We also discuss how their functions are influenced by their chromatin environment and selected cofactors. We consider how, through its multifarious interactions and functionalities, a Mediator-containing and TFIID-containing PIC can yield an integrated signal processing system with the flexibility to determine the unique temporal and spatial expression pattern of a given gene.

Functional partitioning of transcriptional regulators by patterned charge blocks

Components of transcriptional machinery are selectively partitioned into specific condensates, often mediated by protein disorder, yet we know little about how this specificity is achieved. Here, we show that condensates composed of the intrinsically disordered region (IDR) of MED1 selectively partition RNA polymerase II together with its positive allosteric regulators while excluding negative regulators. This selective compartmentalization is sufficient to activate transcription and is required for gene activation during a cell-state transition. The IDRs of partitioned proteins are necessary and sufficient for selective compartmentalization and require alternating blocks of charged amino acids. Disrupting this charge pattern prevents partitioning, whereas adding the pattern to proteins promotes partitioning with functional consequences for gene activation. IDRs with similar patterned charge blocks show similar partitioning and function. These findings demonstrate that disorder-mediated interactions can selectively compartmentalize specific functionally related proteins from a complex mixture of biomolecules, leading to regulation of a biochemical pathway.

Discovery and characterization of orally bioavailable 4-chloro-6-fluoroisophthalamides as covalent PPARG inverse-agonists

PPAR gamma (PPARG) is a ligand activated transcription factor that regulates genes involved in inflammation, bone biology, lipid homeostasis, as well as a master regulator of adipogenesis and a potential lineage driver of luminal bladder cancer. While PPARG agonists lead to transcriptional activation of canonical target genes, inverse agonists have the opposite effect through inducing a transcriptionally repressive complex leading to repression of canonical target gene expression. While many agonists have been described and tested clinically, inverse agonists offer an underexplored avenue to modulate PPARG biology in vivo. Current inverse agonists lack favorable in vivo properties; herein we describe the discovery and characterization of a series of orally bioavailable 4-chloro-6-fluoroisophthalamides as covalent PPARG inverse-agonists, BAY-5516, BAY-5094, and BAY-9683. Structural studies of this series revealed distinct pre- and post-covalent binding positions, which led to the hypothesis that interactions in the pre-covalent conformation are primarily responsible for driving affinity, while interactions in the post-covalent conformation are more responsible for cellular functional effects by enhancing PPARG interactions with its corepressors. The need to simultaneously optimize for two distinct states may partially explain the steep SAR observed. Exquisite selectivity was achieved over related nuclear receptors in the subfamily due in part to a covalent warhead with low reactivity through an S_NAr mechanism in addition to the specificity gained through covalent binding to a reactive cysteine uniquely positioned within the PPARG LBD. BAY-5516, BAY-5094, and BAY-9683 lead to pharmacodynamic regulation of PPARG target gene expression in vivo comparable to known inverse agonist SR10221 and represent new tools for future in vivo studies to explore their potential utility for treatment of disorders of hyperactivated PPARG including luminal bladder cancer and other disorders.

Cdo1 promotes PPARγ-mediated adipose tissue lipolysis in male mice

Cysteine dioxygenase 1 (Cdo1) is a key enzyme in taurine synthesis. Here we show that Cdo1 promotes lipolysis in adipose tissue. Adipose-specific knockout of Cdo1 in mice impairs energy expenditure, cold tolerance and lipolysis, exacerbates diet-induced obesity (DIO) and decreases adipose expression of the key lipolytic genes encoding ATGL and HSL, with little effect on adipose taurine levels. White-adipose-specific overexpression of ATGL and HSL blunts the role of adipose Cdo1 deficiency in promoting DIO. Mechanistically, Cdo1 interacts with PPARγ and facilitates the recruitment of Med24, the core subunit of mediator complex, to ATGL and HSL gene promoters, thereby transactivating their expression. Further, mice with transgenic overexpression of Cdo1 show better cold tolerance, ameliorated DIO and higher lipolysis capacity. Thus, we uncover an unexpected and important role of Cdo1 in regulating adipose lipolysis.

The conserved Mediator subunit cyclin C (CCNC) is required for brown adipocyte development and lipid accumulation

OBJECTIVE

Cyclin C (CCNC) is the most conserved subunit of the Mediator complex, which is an important transcription cofactor. Recently, we have found that CCNC facilitates brown adipogenesis in vitro by activating C/EBPα-dependent transcription. However, the role of CCNC in brown adipose tissue (BAT) in vivo remains unclear.

METHODS

We generated conditional knock-out mice by crossing Ccncflox/flox mice with Myf5Cre, Ucp1Cre or AdipoqCre transgenic mice to investigate the role of CCNC in BAT development and function. We applied glucose and insulin tolerance test, cold exposure and indirect calorimetry to capture the physiological phenotypes and used immunostaining, immunoblotting, qRT-PCR, RNA-seq and cell culture to elucidate the underlying mechanisms.

RESULTS

Here, we show that deletion of CCNC in Myf5+ progenitor cells caused BAT paucity, despite the fact that there was significant neonatal lethality. Mechanistically different from in vitro, CCNC deficiency impaired the proliferation of embryonic brown fat progenitor cells without affecting brown adipogenesis or cell death. Interestingly, CCNC deficiency robustly reduced age-dependent lipid accumulation in differentiated brown adipocytes in all three mouse models. Mechanistically, CCNC in brown adipocytes is required for lipogenic gene expression through the activation of the C/EBPα/GLUT4/ChREBP axis. Consistent with the importance of de novo lipogenesis under carbohydrate-rich diets, high-fat diet (HFD) feeding abolished CCNC deficiency -caused defects of lipid accumulation in BAT. Although insulin sensitivity and response to acute cold exposure were not affected, CCNC deficiency in Ucp1+ cells enhanced the browning of white adipose tissue (beiging) upon prolonged cold exposure.

CONCLUSIONS

Together, these data indicate an important role of CCNC-Mediator in the regulation of BAT development and lipid accumulation in brown adipocytes.

Med23 supports angiogenesis and maintains vascular integrity through negative regulation of angiopoietin2 expression

The mammalian Mediator complex consists of over 30 subunits and functions as a transcriptional hub integrating signaling for tissue-specific gene expression. Although the role of the Mediator complex in transcription has been extensively investigated, the functions of distinct Mediator subunits in development are not well understood. Here, we dissected the role of the Mediator subunit Med23 in mouse cardiovascular development. Endothelial-specific Med23 deletion caused embryonic lethality before embryonic day 13.5 (E13.5). The mutant embryos exhibited intracranial hemorrhage and diminished angiogenesis with dilated blood vessels in the head region, where the expression of Med23 was abundant at E10.5. Med23 deficiency impaired vasculogenesis in the head region and impeded retinal angiogenesis. Knocking down Med23 in human umbilical vein endothelial cells (HUVECs) resulted in angiogenic defects, recapitulating the vascular defects in Med23-mutant mice in a cell-autonomous manner. RNA sequencing in HUVECs indicated that Med23 deficiency resulted in the interruption of angiogenesis and the upregulation of angiopoietin2 (Ang2), an inducing factor for vascular network instability. Inhibition of Ang2 partially rescued angiogenic sprouting and lumen dilation defects in tube formation assays. Collectively, our findings demonstrate that Med23 promotes angiogenesis and maintains vascular integrity, in part by suppressing Ang2 signaling.

Genes and Longevity of Lifespan

Aging is a complex process indicated by low energy levels, declined physiological activity, stress induced loss of homeostasis leading to the risk of diseases and mortality. Recent developments in medical sciences and an increased availability of nutritional requirements has significantly increased the average human lifespan worldwide. Several environmental and physiological factors contribute to the aging process. However, about 40% human life expectancy is inherited among generations, many lifespan associated genes, genetic mechanisms and pathways have been demonstrated during last decades. In the present review, we have evaluated many human genes and their non-human orthologs established for their role in the regulation of lifespan. The study has included more than fifty genes reported in the literature for their contributions to the longevity of life. Intact genomic DNA is essential for the life activities at the level of cell, tissue, and organ. Nucleic acids are vulnerable to oxidative stress, chemotherapies, and exposure to radiations. Efficient DNA repair mechanisms are essential for the maintenance of genomic integrity, damaged DNA is not replicated and transferred to next generations rather the presence of deleterious DNA initiates signaling cascades leading to the cell cycle arrest or apoptosis. DNA modifications, DNA methylation, histone methylation, histone acetylation and DNA damage can eventually lead towards apoptosis. The importance of calorie restriction therapy in the extension of lifespan has also been discussed. The role of pathways involved in the regulation of lifespan such as DAF-16/FOXO (forkhead box protein O1), TOR and JNK pathways has also been particularized. The study provides an updated account of genetic factors associated with the extended lifespan and their interactive contributory role with cellular pathways.

The Oxidative Stress and Chronic Inflammatory Process in Chagas Disease: Role of Exosomes and Contributing Genetic Factors

Chagas disease is a neglected tropical disease caused by the flagellated protozoa Trypanosoma cruzi that affects several million people mainly in Latin American countries. Chagas disease has two phases, which are acute and chronic, both separated by an indeterminate time period in which the infected individual is relatively asymptomatic. The acute phase extends for 40-60 days with atypical and mild symptoms; however, about 30% of the infected patients will develop a symptomatic chronic phase, which is characterized by either cardiac, digestive, neurological, or endocrine problems. Cardiomyopathy is the most important and severe result of Chagas disease, which leads to left ventricular systolic dysfunction, heart failure, and sudden cardiac death. Most deaths are due to heart failure (70%) and sudden death (30%) resulting from cardiomyopathy. During the chronic phase, T. cruzi-infected macrophages respond with the production of proinflammatory cytokines and production of superoxide and nitric oxide by the NADPH oxidase 2 (NOX2) and inducible nitric oxide synthase (iNOS) enzymes, respectively. During the chronic phase, myocardial changes are produced as a result of chronic inflammation, oxidative stress, fibrosis, and cell death. The cellular inflammatory response is mainly the result of activation of the NF-κB-dependent pathway, which activates gene expression of inflammatory cytokines, leading to progressive tissue damage. The persisting production of reactive oxygen species (ROS) is the result of mitochondrial dysfunction in the cardiomyocytes. In this review, we will discuss inflammation and oxidative damage which is produced in the heart during the chronic phase of Chagas disease and recent evidence on the role of macrophages and the production of proinflammatory cytokines during the acute phase and the origin of macrophages/monocytes during the chronic phase of Chagas disease. We will also discuss the contributing factors and mechanisms leading to the chronic inflammation of the cardiac tissue during the chronic phase of the disease as well as the innate and adaptive host immune response. The contribution of genetic factors to the progression of the chronic inflammatory cardiomyopathy of chronic Chagas disease is also discussed. The secreted extracellular vesicles (exosomes) produced for both T. cruzi and infected host cells can play key roles in the host immune response, and those roles are described. Lastly, we describe potential treatments to attenuate the chronic inflammation of the cardiac tissue, designed to improve heart function in chagasic patients.

Galangin 3-benzyl-5-methylether derivatives function as an adiponectin synthesis-promoting peroxisome proliferator-activated receptor γ partial agonist

The upregulation of adiponectin production has been suggested as a novel strategy for the treatment of metabolic diseases. Galangin, a natural flavonoid, exhibited adiponectin synthesis-promoting activity during adipogenesis in human bone marrow mesenchymal stem cells. In target identification, galangin bound both peroxisome proliferator-activated receptor (PPAR) γ and estrogen receptor (ER) β. Novel galangin derivatives were synthesized to improve adiponectin synthesis-promoting compounds by increasing the PPARγ activity of galangin and reducing its ERβ activity, because PPARγ functions can be inhibited by ERβ. Three galangin 3-benzyl-5-methylether derivatives significantly promoted adiponectin production by 2.88-, 4.47-, and 2.76-fold, respectively, compared to the effect of galangin. The most potent compound, galangin 3-benzyl-5,7-dimethylether, selectively bound to PPARγ (Ki, 1.7 μM), whereas it did not bind to ERβ. Galangin 3-benzyl-5,7-dimethylether was identified as a PPARγ partial agonist in docking and pharmacological competition studies, suggesting that it may have diverse therapeutic potential in a variety of metabolic 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.

Role of Peroxisome Proliferator-Activated Receptors (PPARs) in Energy Homeostasis of Dairy Animals: Exploiting Their Modulation through Nutrigenomic Interventions

Peroxisome proliferator-activated receptors (PPARs) are the nuclear receptors that could mediate the nutrient-dependent transcriptional activation and regulate metabolic networks through energy homeostasis. However, these receptors cannot work properly under metabolic stress. PPARs and their subtypes can be modulated by nutrigenomic interventions, particularly under stress conditions to restore cellular homeostasis. Many nutrients such as polyunsaturated fatty acids, vitamins, dietary amino acids and phytochemicals have shown their ability for potential activation or inhibition of PPARs. Thus, through different mechanisms, all these nutrients can modulate PPARs and are ultimately helpful to prevent various metabolic disorders, particularly in transition dairy cows. This review aims to provide insights into the crucial role of PPARs in energy metabolism and their potential modulation through nutrigenomic interventions to improve energy homeostasis in dairy animals.

Usp22 Overexpression Leads to Aberrant Signal Transduction of Cancer-Related Pathways but Is Not Sufficient to Drive Tumor Formation in Mice

Usp22 overexpression is observed in several human cancers and is correlated with poor patient outcomes. The molecular basis underlying this correlation is not clear. Usp22 is the catalytic subunit of the deubiquitylation module in the SAGA histone-modifying complex, which regulates gene transcription. Our previous work demonstrated that the loss of Usp22 in mice leads to decreased expression of several components of receptor tyrosine kinase and TGFβ signaling pathways. To determine whether these pathways are upregulated when Usp22 is overexpressed, we created a mouse model that expresses high levels of Usp22 in all tissues. Phenotypic characterization of these mice revealed over-branching of the mammary glands in females. Transcriptomic analyses indicate the upregulation of key pathways involved in mammary gland branching in mammary epithelial cells derived from the Usp22-overexpressing mice, including estrogen receptor, ERK/MAPK, and TGFβ signaling. However, Usp22 overexpression did not lead to increased tumorigenesis in any tissue. Our findings indicate that elevated levels of Usp22 are not sufficient to induce tumors, but it may enhance signaling abnormalities associated with oncogenesis.

Hyperleptinemia in obese state renders luminal breast cancers refractory to tamoxifen by coordinating a crosstalk between Med1, miR205 and ErbB

Obese women with hormone receptor-positive breast cancer exhibit poor response to therapy and inferior outcomes. However, the underlying molecular mechanisms by which obesity/hyperleptinemia may reduce the efficacy of hormonal therapy remain elusive. Obese mice with hyperleptinemia exhibit increased tumor progression and respond poorly to tamoxifen compared to non-obese mice. Exogenous leptin abrogates tamoxifen-mediated growth inhibition and potentiates breast tumor growth even in the presence of tamoxifen. Mechanistically, leptin induces nuclear translocation of phosphorylated-ER and increases the expression of ER-responsive genes, while reducing tamoxifen-mediated gene repression by abrogating tamoxifen-induced recruitment of corepressors NCoR, SMRT, and Mi2 and potentiating coactivator binding. Furthermore, in silico analysis revealed that coactivator Med1 potentially associates with 48 (out of 74) obesity-signature genes. Interestingly, leptin upregulates Med1 expression by decreasing miR-205, and increases its functional activation via phosphorylation, which is mediated by activation of Her2 and EGFR. It is important to note that Med1 silencing abrogates the negative effects of leptin on tamoxifen efficacy. In addition, honokiol or adiponectin treatment effectively inhibits leptin-induced Med1 expression and improves tamoxifen efficacy in hyperleptinemic state. These studies uncover the mechanistic insights how obese/hyperleptinemic state may contribute to poor response to tamoxifen implicating leptin-miR205-Med1 and leptin-Her2-EGFR-Med1 axes, and present bioactive compound honokiol and adipocytokine adiponectin as agents that can block leptin’s negative effect on tamoxifen.

The Mediator subunit MED20 organizes the early adipogenic complex to promote development of adipose tissues and diet-induced obesity

MED20 is a non-essential subunit of the transcriptional coactivator Mediator complex, but its physiological function remains largely unknown. Here, we identify MED20 as a substrate of the anti-obesity CRL4-WDTC1 E3 ubiquitin ligase complex through affinity purification and candidate screening. Overexpression of WDTC1 leads to degradation of MED20, whereas depletion of WDTC1 or CUL4A/B causes accumulation of MED20. Depleting MED20 inhibits adipogenesis, and a non-degradable MED20 mutant restores adipogenesis in WDTC1-overexpressing cells. Furthermore, knockout of Med20 in preadipocytes abolishes development of brown adipose tissues. Removing one allele of Med20 in preadipocytes protects mice from diet-induced obesity and reverses weight gain in Cul4a- or Cul4b-depleted mice. Chromatin immunoprecipitation sequencing (ChIP-seq) analysis reveals that MED20 organizes the early adipogenic complex by bridging C/EBPβ and RNA polymerase II to promote transcription of the central adipogenic factor, PPARγ. Our findings have thus uncovered a critical role of MED20 in promoting adipogenesis, development of adipose tissue and diet-induced obesity.

Mediator subunit MED1 is required for E2A-PBX1-mediated oncogenic transcription and leukemic cell growth

The chimeric transcription factor E2A-PBX1, containing the N-terminal activation domains of E2A fused to the C-terminal DNA-binding domain of PBX1, results in 5% of pediatric acute lymphoblastic leukemias (ALL). We recently have reported a mechanism for RUNX1-dependent recruitment of E2A-PBX1 to chromatin in pre-B leukemic cells; but the subsequent E2A-PBX1 functions through various coactivators and the general transcriptional machinery remain unclear. The Mediator complex plays a critical role in cell-specific gene activation by serving as a key coactivator for gene-specific transcription factors that facilitates their function through the RNA polymerase II transcriptional machinery, but whether Mediator contributes to aberrant expression of E2A-PBX1 target genes remains largely unexplored. Here we show that Mediator interacts directly with E2A-PBX1 through an interaction of the MED1 subunit with an E2A activation domain. Results of MED1 depletion by CRISPR/Cas9 further indicate that MED1 is specifically required for E2A-PBX1-dependent gene activation and leukemic cell growth. Integrated transcriptome and cistrome analyses identify pre-B cell receptor and cell cycle regulatory genes as direct cotargets of MED1 and E2A-PBX1. Notably, complementary biochemical analyses also demonstrate that recruitment of E2A-PBX1 to a target DNA template involves a direct interaction with DNA-bound RUNX1 that can be further stabilized by EBF1. These findings suggest that E2A-PBX1 interactions with RUNX1 and MED1/Mediator are of functional importance for both gene-specific transcriptional activation and maintenance of E2A-PBX1-driven leukemia. The MED1 dependency for E2A-PBX1-mediated gene activation and leukemogenesis may provide a potential therapeutic opportunity by targeting MED1 in E2A-PBX1⁺ pre-B leukemia.

MED1 is a lipogenesis coactivator required for postnatal adipose expansion

In this study, Jang et al. investigated the role of MED1 in adipose development and expansion in vivo, and they show that MED1 is not generally required for transcription during adipogenesisin culture and that MED1 is dispensable for adipose development in mice. Instead, MED1 is required for postnatal adipose expansion and the induction of fatty acid and triglyceride synthesis genes after pups switch diet from high-fat maternal milk to carbohydrate-based chow. Their findings identify a cell- and gene-specific regulatory role of MED1 as a lipogenesis coactivator required for postnatal adipose expansion.

MED1 often serves as a surrogate of the general transcription coactivator complex Mediator for identifying active enhancers. MED1 is required for phenotypic conversion of fibroblasts to adipocytes in vitro, but its role in adipose development and expansion in vivo has not been reported. Here, we show that MED1 is not generally required for transcription during adipogenesis in culture and that MED1 is dispensable for adipose development in mice. Instead, MED1 is required for postnatal adipose expansion and the induction of fatty acid and triglyceride synthesis genes after pups switch diet from high-fat maternal milk to carbohydrate-based chow. During adipogenesis, MED1 is dispensable for induction of lineage-determining transcription factors (TFs) PPARγ and C/EBPα but is required for lipid accumulation in the late phase of differentiation. Mechanistically, MED1 controls the induction of lipogenesis genes by facilitating lipogenic TF ChREBP- and SREBP1a-dependent recruitment of Mediator to active enhancers. Together, our findings identify a cell- and gene-specific regulatory role of MED1 as a lipogenesis coactivator required for postnatal adipose expansion.

Critical roles of transcriptional coactivator MED1 in the formation and function of mouse adipose tissues

In this study, Ito et al. sought to understand the precise roles of MED1, and its various domains, at various stages of adipogenesis and in adipose tissue. Using multiple genetic approaches to assess requirements for MED1 in adipocyte formation and function in mice, they show that MED1 is indeed essential for the differentiation and/or function of both brown and white adipocytes, as its absence in these cells leads to, respectively, defective brown fat function and lipodystrophy.

The MED1 subunit has been shown to mediate ligand-dependent binding of the Mediator coactivator complex to multiple nuclear receptors, including the adipogenic PPARγ, and to play an essential role in ectopic PPARγ-induced adipogenesis of mouse embryonic fibroblasts. However, the precise roles of MED1, and its various domains, at various stages of adipogenesis and in adipose tissue have been unclear. Here, after establishing requirements for MED1, including specific domains, for differentiation of 3T3L1 cells and both primary white and brown preadipocytes, we used multiple genetic approaches to assess requirements for MED1 in adipocyte formation, maintenance, and function in mice. We show that MED1 is indeed essential for the differentiation and/or function of both brown and white adipocytes, as its absence in these cells leads to, respectively, defective brown fat function and lipodystrophy. This work establishes MED1 as an essential transcriptional coactivator that ensures homeostatic functions of adipocytes.

Hepatocardiac or Cardiohepatic Interaction: From Traditional Chinese Medicine to Western Medicine

There is a close relationship between the liver and heart based on "zang-xiang theory," "five-element theory," and "five-zang/five-viscus/five-organ correlation theory" in the theoretical system of Traditional Chinese Medicine (TCM). Moreover, with the development of molecular biology, genetics, immunology, and others, the Modern Medicine indicates the existence of the essential interorgan communication between the liver and heart (the heart and liver). Anatomically and physiologically, the liver and heart are connected with each other primarily via "blood circulation." Pathologically, liver diseases can affect the heart; for example, patients with end-stage liver disease (liver failure/cirrhosis) may develop into "cirrhotic cardiomyopathy," and nonalcoholic fatty liver disease (NAFLD) may promote the development of cardiovascular diseases via multiple molecular mechanisms. In contrast, heart diseases can affect the liver, heart failure may lead to cardiogenic hypoxic hepatitis and cardiac cirrhosis, and atrial fibrillation (AF) markedly alters the hepatic gene expression profile and induces AF-related hypercoagulation. The heart can also influence liver metabolism via certain nonsecretory cardiac gene-mediated multiple signals. Moreover, organokines are essential mediators of organ crosstalk, e.g., cardiomyokines link the heart to the liver, while hepatokines link the liver to the heart. Therefore, both TCM and Western Medicine, and both the basic research studies and the clinical practices, all indicate that there exist essential "heart-liver axes" and "liver-heart axes." To investigate the organ interactions between the liver and heart (the heart and liver) will help us broaden and deepen our understanding of the pathogenesis of both liver and heart diseases, thus improving the strategies of prevention and treatment in the future.

Mediator structure and conformation change

Mediator is a universal adaptor for transcription control. It serves as an interface between gene-specific activator or repressor proteins and the general RNA polymerase II (pol II) transcription machinery. Previous structural studies revealed a relatively small part of Mediator and none of the gene activator-binding regions. We have determined the cryo-EM structure of the Mediator at near-atomic resolution. The structure reveals almost all amino acid residues in ordered regions, including the major targets of activator proteins, the Tail module, and the Med1 subunit of the Middle module. Comparison of Mediator structures with and without pol II reveals conformational changes that propagate across the entire Mediator, from Head to Tail, coupling activator- and pol II-interacting regions.

Discovery and Structure-Activity Relationships of Novel Template, Truncated 1'-Homologated Adenosine Derivatives as Pure Dual PPARγ/δ Modulators

Following our report that A₃ adenosine receptor (AR) antagonist 1 exhibited a polypharmacological profile as a dual modulator of peroxisome proliferator-activated receptor (PPAR)γ/δ, we discovered a new template, 1'-homologated adenosine analogues 4a-4t, as dual PPARγ/δ modulators without AR binding. Removal of binding affinity to A₃AR was achieved by 1'-homologation, and PPARγ/δ dual modulation was derived from the structural similarity between the target nucleosides and PPAR modulator drug, rosiglitazone. All the final nucleosides were devoid of AR-binding affinity and exhibited high binding affinities to PPARγ/δ but lacked PPARα binding. 2-Cl derivatives exhibited dual receptor-binding affinity to PPARγ/δ, which was absent for the corresponding 2-H derivatives. 2-Propynyl substitution prevented PPARδ-binding affinity but preserved PPARγ affinity, indicating that the C2 position defines a pharmacophore for selective PPARγ ligand designs. PPARγ/δ dual modulators functioning as both PPARγ partial agonists and PPARδ antagonists promoted adiponectin production, suggesting their therapeutic potential against hypoadiponectinemia-associated cancer and metabolic diseases.

Molecular determinants of MED1 interaction with the DNA bound VDR-RXR heterodimer

The MED1 subunit of the Mediator complex is an essential coactivator of nuclear receptor-mediated transcriptional activation. While structural requirements for ligand-dependent binding of classical coactivator motifs of MED1 to numerous nuclear receptor ligand-binding domains have been fully elucidated, the recognition of the full-length or truncated coactivator by full nuclear receptor complexes remain unknown. Here we present structural details of the interaction between a large part of MED1 comprising its structured N-terminal and the flexible receptor-interacting domains and the mutual heterodimer of the vitamin D receptor (VDR) and the retinoid X receptor (RXR) bound to their cognate DNA response element. Using a combination of structural and biophysical methods we show that the ligand-dependent interaction between VDR and the second coactivator motif of MED1 is crucial for complex formation and we identify additional, previously unseen, interaction details. In particular, we identified RXR regions involved in the interaction with the structured N-terminal domain of MED1, as well as VDR regions outside the classical coactivator binding cleft affected by coactivator recruitment. These findings highlight important roles of each receptor within the heterodimer in selective recognition of MED1 and contribute to our understanding of the nuclear receptor-coregulator complexes.

MED19 Regulates Adipogenesis and Maintenance of White Adipose Tissue Mass by Mediating PPARγ-Dependent Gene Expression

The Mediator complex relays regulatory signals from gene-specific transcription factors to the basal transcriptional machinery. However, the role of individual Mediator subunits in different tissues remains unclear. Here, we demonstrate that MED19 is essential for adipogenesis and maintenance of white adipose tissue (WAT) by mediating peroxisome proliferator-activated receptor gamma (PPARγ) transcriptional activity. MED19 knockdown blocks white adipogenesis, but not brown adipogenesis or C2C12 myoblast differentiation. Adipose-specific MED19 knockout (KO) in mice results in a striking loss of WAT, whitening of brown fat, hepatic steatosis, and insulin resistance. Inducible adipose-specific MED19 KO in adult animals also results in lipodystrophy, demonstrating its requirement for WAT maintenance. Global gene expression analysis reveals induction of genes involved in apoptosis and inflammation and impaired expression of adipose-specific genes, resulting from decreased PPARγ residency on adipocyte gene promoters and reduced association of PPARγ with RNA polymerase II. These results identify MED19 as a crucial facilitator of PPARγ-mediated gene expression in adipose tissue.

RNF20 Functions as a Transcriptional Coactivator for PPARγ by Promoting NCoR1 Degradation in Adipocytes

Adipose tissue is the key organ coordinating whole-body energy homeostasis. Although it has been reported that ring finger protein 20 (RNF20) regulates lipid metabolism in the liver and kidney, the roles of RNF20 in adipose tissue have not been explored. Here, we demonstrate that RNF20 promotes adipogenesis by potentiating the transcriptional activity of peroxisome proliferator-activated receptor-γ (PPARγ). Under normal chow diet feeding, Rnf20 defective (Rnf20 ^+/- ) mice exhibited reduced fat mass with smaller adipocytes compared with wild-type littermates. In addition, high-fat diet-fed Rnf20 ^+/- mice alleviated systemic insulin resistance accompanied by a reduced expansion of fat tissue. Quantitative proteomic analyses revealed significantly decreased levels of PPARγ target proteins in adipose tissue of Rnf20 ^+/- mice. Mechanistically, RNF20 promoted proteasomal degradation of nuclear corepressor 1 (NCoR1), which led to stimulation of the transcriptional activity of PPARγ. Collectively, these data suggest that RNF20-NCoR1 is a novel axis in adipocyte biology through fine-tuning the transcriptional activity of PPARγ.

miR‑146a improves hepatic lipid and glucose metabolism by targeting MED1

Non-alcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases worldwide. Increasing evidence has shown that microRNAs (miRNAs) play a vital role in the progression of NAFLD. The aim of the present study was to examine the expression level and roles of miR-146a in fatty liver of high-fat diet (HFD) and ob/ob mice and fatty acid-treated hepatic cells using RT-qPCR and western blot analysis. The results showed that the expression of miR-146a was significantly decreased in the livers of high-fat diet (HFD) and ob/ob mice and free fatty acid-stimulated cells by RT-qPCR. Overexpression of hepatic miR-146a improved glucose and insulin tolerance as well as lipid accumulation in the liver by promoting the oxidative metabolism of fatty acids. In addition, the overexpression of miR-146a increased the amount of mitochondria and promoted mitochondrial respiration in hepatocytes. Similarly, inhibition of miR-146a expression levels significantly reduced mitochondrial numbers in AML12 cells as well as the expression of mitochondrial respiration related genes. Additionally, MED1 was a direct target of miR-146a and restoring MED1 abolished the metabolic effects of miR-146a on lipid metabolism and mitochondrial function. Therefore, results of the present study identified a novel function of miR-146a in glucose and lipid metabolism in targeting MED1, suggesting that miR-146a serves as a potential therapeutic target for metabolic syndrome disease.

A novel specific peroxisome proliferator-activated receptor γ (PPARγ) modulator YR4-42 ameliorates hyperglycaemia and dyslipidaemia and hepatic steatosis in diet-induced obese mice

AIMS

To evaluate a novel tetrahydroisoquinoline derivative YR4-42 as a selective peroxisome proliferator-activated receptor γ (PPARγ) modulator (SPPARM) and explore its anti-diabetic effects in vitro and in vivo.

MATERIALS AND METHODS

Using two standard full PPARγ agonists rosiglitazone and pioglitazone as controls, the PPARγ binding affinity and transactivation action of YR4-42 were evaluated using biochemical and cell-based reporter gene assays. The capacity of YR4-42 to recruit coactivators of PPARγ was also assessed. The effects of YR4-42 on adipogenesis and glucose consumption and PPARγ Ser273 phosphorylation were investigated in 3T3-L1 adipocytes. The effects of YR4-42 and pioglitazone, serving as positive control, on glucose and lipids metabolism were investigated in high-fat diet-induced obese (DIO) C57BL/6J mice. The expression of PPARγ target genes involved in glucose and lipid metabolism was also assessed in vitro and in vivo.

RESULTS

In vitro biochemical and cell-based functional assays showed that YR4-42 has much weaker binding affinity, transactivation, and recruitment to PPARγ of the coactivators thyroid hormone receptor-associated protein complex 220 kDa component (TRAP220) and PPARγ coactivator 1-α (PGC1α) compared to full agonists. In 3 T3-L1 adipocytes, YR4-42 significantly improved glucose consumption without a lipogenesis effect, while blocking tumour necrosis factor α-mediated phosphorylation of PPARγ at Ser273, thereby upregulating the expression of the PPARγ Ser273 phosphorylation-dependent genes. Furthermore, in DIO mice, oral administration of YR4-42 ameliorated the hyperglycaemia, with a similar insulin sensitization effect to that of pioglitazone. Importantly, YR4-42 also improved hyperlipidaemia-associated hepatic steatosis without weight gain, which avoids a major side effect of pioglitazone. Thus, YR4-42 appeared to selectively modulate PPARγ responses. This finding was supported by the gene expression analysis, which showed that YR4-42 selectively targets PPARγ-regulated genes mapped to glucose and lipid metabolism in DIO mice.

CONCLUSIONS

We conclude that YR4-42 is a novel anti-diabetic drug candidate with significant advantages compared to standard PPARγ agonists. YR4-42 should be further investigated in preclinical and clinical studies.

Quantitative structural assessment of graded receptor agonism

Ligand-receptor interactions, which are ubiquitous in physiology, are described by theoretical models of receptor pharmacology. Structural evidence for graded efficacy receptor conformations predicted by receptor theory has been limited but is critical to fully validate theoretical models. We applied quantitative structure-function approaches to characterize the effects of structurally similar and structurally diverse agonists on the conformational ensemble of nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ). For all ligands, agonist functional efficacy is correlated to a shift in the conformational ensemble equilibrium from a ground state toward an active state, which is detected by NMR spectroscopy but not observed in crystal structures. For the structurally similar ligands, ligand potency and affinity are also correlated to efficacy and conformation, indicating ligand residence times among related analogs may influence receptor conformation and function. Our results derived from quantitative graded activity-conformation correlations provide experimental evidence and a platform with which to extend and test theoretical models of receptor pharmacology to more accurately describe and predict ligand-dependent receptor activity.

50+ years of eukaryotic transcription: an expanding universe of factors and mechanisms

The landmark 1969 discovery of nuclear RNA polymerases I, II and III in diverse eukaryotes represented a major turning point in the field that, with subsequent elucidation of the distinct structures and functions of these enzymes, catalyzed an avalanche of further studies. In this Review, written from a personal and historical perspective, I highlight foundational biochemical studies that led to the discovery of an expanding universe of the components of the transcriptional and regulatory machineries, and a parallel complexity in gene-specific mechanisms that continue to be explored to the present day.

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.

Structural Basis of Altered Potency and Efficacy Displayed by a Major in Vivo Metabolite of the Antidiabetic PPARγ Drug Pioglitazone

Pioglitazone (Pio) is a Food and Drug Administration-approved drug for type-2 diabetes that binds and activates the nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ), yet it remains unclear how in vivo Pio metabolites affect PPARγ structure and function. Here, we present a structure-function comparison of Pio and its most abundant in vivo metabolite, 1-hydroxypioglitazone (PioOH). PioOH displayed a lower binding affinity and reduced potency in co-regulator recruitment assays. X-ray crystallography and molecular docking analysis of PioOH-bound PPARγ ligand-binding domain revealed an altered hydrogen bonding network, including the formation of water-mediated bonds, which could underlie its altered biochemical phenotype. NMR spectroscopy and hydrogen/deuterium exchange mass spectrometry analysis coupled to activity assays revealed that PioOH better stabilizes the PPARγ activation function-2 (AF-2) co-activator binding surface and better enhances co-activator binding, affording slightly better transcriptional efficacy. These results indicating that Pio hydroxylation affects its potency and efficacy as a PPARγ agonist contributes to our understanding of PPARγ-drug metabolite interactions.

TET2 facilitates PPARγ agonist-mediated gene regulation and insulin sensitization in adipocytes

Emerging evidence indicates that epigenetic mechanisms like DNA methylation directly contribute to metabolic regulation. For example, we previously demonstrated that de novo DNA methyltransferase Dnmt3a plays a causal role in the development of adipocyte insulin resistance. Recent studies suggest that DNA demethylation plays an important role in the developmental process of adipocytes. However, little is known about whether DNA demethylase ten-eleven translocation (TET) proteins regulate the metabolic functions of adipocytes.

METHODS

The expression of Tet genes was assessed in the fractionated adipocytes of chow- and high fat diet-fed C57/Bl6 mice using qPCR and western blotting. The effect of Tet2 gain- or loss-of-function in fully mature 3T3-L1 adipocytes in the presence/absence of Rosiglitazone (Rosi) and TNF-α on insulin sensitivity was using the insulin-stimulated glucose uptake and insulin signaling assays. Gene expression and DNA methylation analyses of PPARγ target genes was performed in the same setting. In addition, PPARγ reporter assays, co-immunoprecipitation assays, PPARγ ChIP-PCR analyses were performed.

RESULTS

We found that adipose expression of TET2, alone among its family members, was significantly reduced in diet-induced insulin resistance. TET2 gain-of-function was sufficient to promote insulin sensitivity while loss-of-function was necessary to facilitate insulin sensitization in response to the PPARγ agonist Rosiglitazone (Rosi) in cultured adipocytes. Consistent with this, TET2 was required for Rosi-dependent gene activation of certain PPARγ targets accompanied by changes in DNA demethylation at the promoter regions. Furthermore, TET2 was necessary to sustain PPARγ binding to target loci upon activation with Rosi via physical interaction with PPARγ.

CONCLUSIONS

Our data demonstrate that TET2 works as an epigenetic regulator of Rosi-mediated insulin sensitization and transcriptional regulation in adipocytes.

A structural mechanism for directing corepressor-selective inverse agonism of PPARγ

Small chemical modifications can have significant effects on ligand efficacy and receptor activity, but the underlying structural mechanisms can be difficult to predict from static crystal structures alone. Here we show how a simple phenyl-to-pyridyl substitution between two common covalent orthosteric ligands targeting peroxisome proliferator-activated receptor (PPAR) gamma converts a transcriptionally neutral antagonist (GW9662) into a repressive inverse agonist (T0070907) relative to basal cellular activity. X-ray crystallography, molecular dynamics simulations, and mutagenesis coupled to activity assays reveal a water-mediated hydrogen bond network linking the T0070907 pyridyl group to Arg288 that is essential for corepressor-selective inverse agonism. NMR spectroscopy reveals that PPARγ exchanges between two long-lived conformations when bound to T0070907 but not GW9662, including a conformation that prepopulates a corepressor-bound state, priming PPARγ for high affinity corepressor binding. Our findings demonstrate that ligand engagement of Arg288 may provide routes for developing corepressor-selective repressive PPARγ ligands.

Peroxisome proliferator-activated receptor gamma (PPARγ) is a target for insulin sensitizing drugs. Here the authors combine NMR, X-ray crystallography and MD simulations and report a structural mechanism for eliciting PPARγ inverse agonism, where coactivator binding is inhibited and corepressor binding promoted, which causes PPARγ repression.

Intestinal bile acid sequestration improves glucose control by stimulating hepatic miR-182-5p in type 2 diabetes

Colesevelam is a bile acid sequestrant approved to treat both hyperlipidemia and type 2 diabetes, but the mechanism for its glucose-lowering effects is not fully understood. The aim of this study was to investigate the role of hepatic microRNAs (miRNAs) as regulators of metabolic disease and to investigate the link between the cholesterol and glucose-lowering effects of colesevelam. To quantify the impact of colesevelam treatment in rodent models of diabetes, metabolic studies were performed in Zucker diabetic fatty (ZDF) rats and db/db mice. Colesevelam treatments significantly decreased plasma glucose levels and increased glycolysis in the absence of changes to insulin levels in ZDF rats and db/db mice. High-throughput sequencing and real-time PCR were used to quantify hepatic miRNA and mRNA changes, and the cholesterol-sensitive miR-96/182/183 cluster was found to be significantly increased in livers from ZDF rats treated with colesevelam compared with vehicle controls. Inhibition of miR-182 in vivo attenuated colesevelam-mediated improvements to glycemic control in db/db mice. Hepatic expression of mediator complex subunit 1 (MED1), a nuclear receptor coactivator, was significantly decreased with colesevelam treatments in db/db mice, and MED1 was experimentally validated to be a direct target of miR-96/182/183 in humans and mice. In summary, these results support that colesevelam likely improves glycemic control through hepatic miR-182-5p, a mechanism that directly links cholesterol and glucose metabolism. NEW & NOTEWORTHY Colesevelam lowers systemic glucose levels in Zucker diabetic fatty rats and db/db mice and increases hepatic levels of the sterol response element binding protein 2-responsive microRNA cluster miR-96/182/183. Inhibition of miR-182 in vivo reverses the glucose-lowering effects of colesevelam in db/db mice. Mediator complex subunit 1 (MED1) is a novel, direct target of the miR-96/182/183 cluster in mice and humans.

Development of an In Vitro Screening Platform for the Identification of Partial PPARγ Agonists as a Source for Antidiabetic Lead Compounds

Type 2 diabetes (T2D) is a metabolic disorder where insulin-sensitive tissues show reduced sensitivity towards insulin and a decreased glucose uptake (GU), which leads to hyperglycaemia. Peroxisome proliferator-activated receptor (PPAR)γ plays an important role in lipid and glucose homeostasis and is one of the targets in the discovery of drugs against T2D. Activation of PPARγ by agonists leads to a conformational change in the ligand-binding domain, a process that alters the transcription of several target genes involved in glucose and lipid metabolism. Depending on the ligands, they can induce different sets of genes that depends of their recruitment of coactivators. The activation of PPARγ by full agonists such as the thiazolidinediones leads to improved insulin sensitivity but also to severe side effects probably due to their behavior as full agonists. Partial PPARγ agonists are compounds with diminished agonist efficacy compared to full agonist that may exhibit the same antidiabetic effect as full agonists without inducing the same magnitude of side effects. In this review, we describe a screening platform for the identification of partial PPARγ agonists from plant extracts that could be promising lead compounds for the development of antidiabetic drugs. The screening platform includes a series of in vitro bioassays, such as GU in adipocytes, PPARγ-mediated transactivation, adipocyte differentiation and gene expression as well as in silico docking for partial PPARγ agonism.

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.

Depletion of Nsd2-mediated histone H3K36 methylation impairs adipose tissue development and function

The epigenetic mechanisms regulating adipose tissue development and function are poorly understood. In this study, we show that depletion of histone H3K36 methylation by H3.3K36M in preadipocytes inhibits adipogenesis by increasing H3K27me3 to prevent the induction of C/EBPα and other targets of the master adipogenic transcription factor peroxisome proliferator-activated receptor-γ (PPARγ). Depleting H3K36 methyltransferase Nsd2, but not Nsd1 or Setd2, phenocopies the effects of H3.3K36M on adipogenesis and PPARγ target expression. Consistently, expression of H3.3K36M in progenitor cells impairs brown adipose tissue (BAT) and muscle development in mice. In contrast, depletion of histone H3K36 methylation by H3.3K36M in adipocytes in vivo does not affect adipose tissue weight, but leads to profound whitening of BAT and insulin resistance in white adipose tissue (WAT). These mice are resistant to high fat diet-induced WAT expansion and show severe lipodystrophy. Together, these results suggest a critical role of Nsd2-mediated H3K36 methylation in adipose tissue development and function.

Differential effects of dietary flavonoids on adipogenesis

Propose

Obesity is a fast growing epidemic worldwide. During obesity, the increase in adipose tissue mass arise from two different mechanisms, namely, hyperplasia and hypertrophy. Hyperplasia which is the increase in adipocyte number is characteristic of severe obese patients. Recently, there has been much interest in targeting adipogenesis as therapeutic strategy against obesity. Flavonoids have been shown to regulate several pathways and affect a number of molecular targets during specific stages of adipocyte development.

Methods

Presently, we provide a review of key studies evaluating the effects of dietary flavonoids in different stages of adipocyte development with a particular emphasis on the investigations that explore the underlying mechanisms of action of these compounds in human or animal cell lines as well as animal models.

Results

Flavonoids have been shown to regulate several pathways and affect a number of molecular targets during specific stages of adipocyte development. Although most of the studies reveal anti-adipogenic effect of flavonoids, some flavonoids demonstrated proadipogenic effect in mesenchymal stem cells or preadipocytes.

Conclusion

The anti-adipogenic effect of flavonoids is mainly via their effect on regulation of several pathways such as induction of apoptosis, suppression of key adipogenic transcription factors, activation of AMPK and Wnt pathways, inhibition of clonal expansion, and cell-cycle arrest.

Control of Muscle Metabolism by the Mediator Complex

Exercise represents an energetic challenge to whole-body homeostasis. In skeletal muscle, exercise activates a variety of signaling pathways that culminate in the nucleus to regulate genes involved in metabolism and contractility; however, much remains to be learned about the transcriptional effectors of exercise. Mediator is a multiprotein complex that links signal-dependent transcription factors and other transcriptional regulators with the basal transcriptional machinery, thereby serving as a transcriptional "hub." In this article, we discuss recent studies highlighting the role of Mediator subunits in metabolic regulation and glucose metabolism, as well as exercise responsiveness. Elucidation of the roles of Mediator subunits in metabolic control has revealed new mechanisms and molecular targets for the modulation of metabolism and metabolic disorders.

Therapeutic potential of Mediator complex subunits in metabolic diseases

The multisubunit Mediator is an evolutionary conserved transcriptional coregulatory complex in eukaryotes. It is needed for the transcriptional regulation of gene expression in general as well as in a gene specific manner. Mediator complex subunits interact with different transcription factors as well as components of RNA Pol II transcription initiation complex and in doing so act as a bridge between gene specific transcription factors and general Pol II transcription machinery. Specific interaction of various Mediator subunits with nuclear receptors (NRs) and other transcription factors involved in metabolism has been reported in different studies. Evidences indicate that ligand-activated NRs recruit Mediator complex for RNA Pol II-dependent gene transcription. These NRs have been explored as therapeutic targets in different metabolic diseases; however, they show side-effects as targets due to their overlapping involvement in different signaling pathways. Here we discuss the interaction of various Mediator subunits with transcription factors involved in metabolism and whether specific interaction of these transcription factors with Mediator subunits could be potentially utilized as therapeutic strategy in a variety of metabolic diseases.

ETV4 and AP1 Transcription Factors Form Multivalent Interactions with three Sites on the MED25 Activator-Interacting Domain

The recruitment of transcriptional cofactors by sequence-specific transcription factors challenges the basis of high affinity and selective interactions. Extending previous studies that the N-terminal activation domain (AD) of ETV5 interacts with Mediator subunit 25 (MED25), we establish that similar, aromatic-rich motifs located both in the AD and in the DNA-binding domain (DBD) of the related ETS factor ETV4 interact with MED25. These ETV4 regions bind MED25 independently, display distinct kinetics, and combine to contribute to a high-affinity interaction of full-length ETV4 with MED25. High-affinity interactions with MED25 are specific for the ETV1/4/5 subfamily as other ETS factors display weaker binding. The AD binds to a single site on MED25 and the DBD interacts with three MED25 sites, allowing for simultaneous binding of both domains in full-length ETV4. MED25 also stimulates the in vitro DNA binding activity of ETV4 by relieving autoinhibition. ETV1/4/5 factors are often overexpressed in prostate cancer and genome-wide studies in a prostate cancer cell line indicate that ETV4 and MED25 occupy enhancers that are enriched for ETS-binding sequences and are both functionally important for the transcription of genes regulated by these enhancers. AP1-motifs, which bind JUN and FOS transcription factor families, were observed in MED25-occupied regions and JUN/FOS also contact MED25; FOS strongly binds to the same MED25 site as ETV4 AD and JUN interacts with the other two MED25 sites. In summary, we describe features of the multivalent ETV4- and AP1-MED25 interactions, thereby implicating these factors in the recruitment of MED25 to transcriptional control elements.

Mediator 1 Is Atherosclerosis Protective by Regulating Macrophage Polarization

OBJECTIVE

MED1 (mediator 1) interacts with transcription factors to regulate transcriptional machinery. The role of MED1 in macrophage biology and the relevant disease state remains to be investigated.

APPROACH AND RESULTS

To study the molecular mechanism by which MED1 regulates the M1/M2 phenotype switch of macrophage and the effect on atherosclerosis, we generated MED1/apolipoprotein E (ApoE) double-deficient (MED1^ΔMac/ApoE^-/-) mice and found that atherosclerosis was greater in MED1^ΔMac/ApoE^-/- mice than in MED1^fl/fl/ApoE^-/- littermates. The gene expression of M1 markers was increased and that of M2 markers decreased in both aortic wall and peritoneal macrophages from MED1^ΔMac/ApoE^-/- mice, whereas MED1 overexpression rectified the changes in M1/M2 expression. Moreover, LDLR (low-density lipoprotein receptor)-deficient mice received bone marrow from MED1^ΔMac mice showed greater atherosclerosis. Mechanistically, MED1 ablation decreased the binding of PPARγ (peroxisome proliferator-activated receptor γ) and enrichment of H3K4me1 and H3K27ac to upstream region of M2 marker genes. Furthermore, interleukin 4 induction of PPARγ and MED1 increased the binding of PPARγ or MED1 to the PPAR response elements of M2 marker genes.

CONCLUSIONS

Our data suggest that MED1 is required for the PPARγ-mediated M2 phenotype switch, with M2 marker genes induced but M1 marker genes suppressed. MED1 in macrophages has an antiatherosclerotic role via PPARγ-regulated transactivation.

Cyclin C regulates adipogenesis by stimulating transcriptional activity of CCAAT/enhancer-binding protein α

Brown adipose tissue is important for maintaining energy homeostasis and adaptive thermogenesis in rodents and humans. As disorders arising from dysregulated energy metabolism, such as obesity and metabolic diseases, have increased, so has interest in the molecular mechanisms of adipocyte biology. Using a functional screen, we identified cyclin C (CycC), a conserved subunit of the Mediator complex, as a novel regulator for brown adipocyte formation. siRNA-mediated CycC knockdown (KD) in brown preadipocytes impaired the early transcriptional program of differentiation, and genetic KO of CycC completely blocked the differentiation process. RNA sequencing analyses of CycC-KD revealed a critical role of CycC in activating genes co-regulated by peroxisome proliferator activated receptor γ (PPARγ) and CCAAT/enhancer-binding protein α (C/EBPα). Overexpression of PPARγ2 or addition of the PPARγ ligand rosiglitazone rescued the defects in CycC-KO brown preadipocytes and efficiently activated the PPARγ-responsive promoters in both WT and CycC-KO cells, suggesting that CycC is not essential for PPARγ transcriptional activity. In contrast, CycC-KO significantly reduced C/EBPα-dependent gene expression. Unlike for PPARγ, overexpression of C/EBPα could not induce C/EBPα target gene expression in CycC-KO cells or rescue the CycC-KO defects in brown adipogenesis, suggesting that CycC is essential for C/EBPα-mediated gene activation. CycC physically interacted with C/EBPα, and this interaction was required for C/EBPα transactivation domain activity. Consistent with the role of C/EBPα in white adipogenesis, CycC-KD also inhibited differentiation of 3T3-L1 cells into white adipocytes. Together, these data indicate that CycC activates adipogenesis in part by stimulating the transcriptional activity of C/EBPα.

Regulatory Enhancer-Core-Promoter Communication via Transcription Factors and Cofactors

Gene expression is regulated by genomic enhancers that recruit transcription factors and cofactors to activate transcription from target core promoters. Over the past years, thousands of enhancers and core promoters in animal genomes have been annotated, and we have learned much about the domain structure in which regulatory genomes are organized in animals. Enhancer-core-promoter targeting occurs at several levels, including regulatory domains, DNA accessibility, and sequence-encoded core-promoter specificities that are likely mediated by different regulatory proteins. We review here current knowledge about enhancer-core-promoter targeting, regulatory communication between enhancers and core promoters, and the protein factors involved. We conclude with an outlook on open questions that we find particularly interesting and that will likely lead to additional insights in the upcoming years.

Regulation of metabolism by the Mediator complex

The Mediator complex was originally discovered in yeast, but it is conserved in all eukaryotes. Its best-known function is to regulate RNA polymerase II-dependent gene transcription. Although the mechanisms by which the Mediator complex regulates transcription are often complicated by the context-dependent regulation, this transcription cofactor complex plays a pivotal role in numerous biological pathways. Biochemical, molecular, and physiological studies using cancer cell lines or model organisms have established the current paradigm of the Mediator functions. However, the physiological roles of the mammalian Mediator complex remain poorly defined, but have attracted a great interest in recent years. In this short review, we will summarize some of the reported functions of selective Mediator subunits in the regulation of metabolism. These intriguing findings suggest that the Mediator complex may be an important player in nutrient sensing and energy balance in mammals.