The nuclear receptor corepressors NCoR and SMRT decrease peroxisome proliferator-activated receptor gamma transcriptional activity and repress 3T3-L1 adipogenesis

Bifidobacterium bifidum Strain BB1 Inhibits Tumor Necrosis Factor-α-Induced Increase in Intestinal Epithelial Tight Junction Permeability via Toll-Like Receptor-2/Toll-Like Receptor-6 Receptor Complex-Dependent Stimulation of Peroxisome Proliferator-Activated Receptor γ and Suppression of NF-κB p65

Bifidobacterium bifidum strain BB1 causes a strain-specific enhancement in intestinal epithelial tight junction (TJ) barrier. Tumor necrosis factor (TNF)-α induces an increase in intestinal epithelial TJ permeability and promotes intestinal inflammation. The major purpose of this study was to delineate the protective effect of BB1 against the TNF-α-induced increase in intestinal TJ permeability and to unravel the intracellular mechanisms involved. TNF-α produces an increase in intestinal epithelial TJ permeability in Caco-2 monolayers and in mice. Herein, the addition of BB1 inhibited the TNF-α increase in Caco-2 intestinal TJ permeability and mouse intestinal permeability in a strain-specific manner. BB1 inhibited the TNF-α-induced increase in intestinal TJ permeability by interfering with TNF-α-induced enterocyte NF-κB p50/p65 and myosin light chain kinase (MLCK) gene activation. The BB1 protective effect against the TNF-α-induced increase in intestinal permeability was mediated by toll-like receptor-2/toll-like receptor-6 heterodimer complex activation of peroxisome proliferator-activated receptor γ (PPAR-γ) and PPAR-γ pathway inhibition of TNF-α-induced inhibitory kappa B kinase α (IKK-α) activation, which, in turn, resulted in a step-wise inhibition of NF-κB p50/p65, MLCK gene, MLCK kinase activity, and MLCK-induced opening of the TJ barrier. In conclusion, these studies unraveled novel intracellular mechanisms of BB1 protection against the TNF-α-induced increase in intestinal TJ permeability. The current data show that BB1 protects against the TNF-α-induced increase in intestinal epithelial TJ permeability via a PPAR-γ-dependent inhibition of NF-κB p50/p65 and MLCK gene activation.

Cell-state dependent regulation of PPAR γ signaling by ZBTB9 in adipocytes

Adipocytes play a critical role in metabolic homeostasis. Peroxisome proliferator-activated receptor- γ (PPAR γ ) is a nuclear hormone receptor that is a master regulator of adipocyte differentiation and function. ZBTB9 was predicted to interact with PPAR γ based on large-scale protein interaction experiments. In addition, GWAS studies in the type 2 diabetes (T2D) Knowledge Portal revealed associations between Z btb9 and both BMI and T2D risk. Here we show that ZBTB9 positively regulates PPAR γ activity in mature adipocytes. Surprisingly Z btb9 knockdown (KD) also increased adipogenesis in 3T3-L1 cells and human preadipocytes. E2F activity was increased and E2F downstream target genes were upregulated in Zbtb9 -KD preadipocytes. Accordingly, RB phosphorylation, which regulates E2F activity, was enhanced in Zbtb9 -KD preadipocytes. Critically, an E2F1 inhibitor blocked the effects of Zbtb9 deficiency on adipogenic gene expression and lipid accumulation. Collectively, these results demonstrate that Zbtb9 inhibits adipogenesis as a negative regulator of Pparg expression via altered RB-E2F1 signaling. Our findings reveal complex cell-state dependent roles of ZBTB9 in adipocytes, identifying a new molecule that regulates adipogenesis and adipocyte biology as both a positive and negative regulator of PPAR γ signaling depending on the cellular context, and thus may be important in the pathogenesis and treatment of obesity and T2D.

An intronic enhancer of Cebpa regulates adipocyte differentiation and adipose tissue development via long-range loop formation

Cebpa is a master transcription factor gene for adipogenesis. However, the mechanisms of enhancer-promoter chromatin interactions controlling Cebpa transcriptional regulation during adipogenic differentiation remain largely unknown. To reveal how the three-dimensional structure of Cebpa changes during adipogenesis, we generated high-resolution chromatin interactions of Cebpa in 3T3-L1 preadipocytes and 3T3-L1 adipocytes using circularized chromosome conformation capture sequencing (4C-seq). We revealed dramatic changes in chromatin interactions and chromatin status at interaction sites during adipogenic differentiation. Based on this, we identified five active enhancers of Cebpa in 3T3-L1 adipocytes through epigenomic data and luciferase reporter assays. Next, epigenetic repression of Cebpa-L1-AD-En2 or -En3 by the dCas9-KRAB system significantly down-regulated Cebpa expression and inhibited adipocyte differentiation. Furthermore, experimental depletion of cohesin decreased the interaction intensity between Cebpa-L1-AD-En2 and the Cebpa promoter and down-regulated Cebpa expression, indicating that long-range chromatin loop formation was mediated by cohesin. Two transcription factors, RXRA and PPARG, synergistically regulate the activity of Cebpa-L1-AD-En2. To test whether Cebpa-L1-AD-En2 plays a role in adipose tissue development, we injected dCas9-KRAB-En2 lentivirus into the inguinal white adipose tissue (iWAT) of mice to suppress the activity of Cebpa-L1-AD-En2. Repression of Cebpa-L1-AD-En2 significantly decreased Cebpa expression and adipocyte size, altered iWAT transcriptome, and affected iWAT development. We identified functional enhancers regulating Cebpa expression and clarified the crucial roles of Cebpa-L1-AD-En2 and Cebpa promoter interaction in adipocyte differentiation and adipose tissue development.

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.

Peroxisome proliferator-activated receptor ɣ agonist mediated inhibition of heparanase expression reduces proteinuria

BACKGROUND

Proteinuria is associated with many glomerular diseases and a risk factor for the progression to renal failure. We previously showed that heparanase (HPSE) is essential for the development of proteinuria, whereas peroxisome proliferator-activated receptor ɣ (PPARɣ) agonists can ameliorate proteinuria. Since a recent study showed that PPARɣ regulates HPSE expression in liver cancer cells, we hypothesized that PPARɣ agonists exert their reno-protective effect by inhibiting glomerular HPSE expression.

METHODS

Regulation of HPSE by PPARɣ was assessed in the adriamycin nephropathy rat model, and cultured glomerular endothelial cells and podocytes. Analyses included immunofluorescence staining, real-time PCR, heparanase activity assay and transendothelial albumin passage assay. Direct binding of PPARɣ to the HPSE promoter was evaluated by the luciferase reporter assay and chromatin immunoprecipitation assay. Furthermore, HPSE activity was assessed in 38 type 2 diabetes mellitus (T2DM) patients before and after 16/24 weeks treatment with the PPARɣ agonist pioglitazone.

FINDINGS

Adriamycin-exposed rats developed proteinuria, an increased cortical HPSE and decreased heparan sulfate (HS) expression, which was ameliorated by treatment with pioglitazone. In line, the PPARɣ antagonist GW9662 increased cortical HPSE and decreased HS expression, accompanied with proteinuria in healthy rats, as previously shown. In vitro, GW9662 induced HPSE expression in both endothelial cells and podocytes, and increased transendothelial albumin passage in a HPSE-dependent manner. Pioglitazone normalized HPSE expression in adriamycin-injured human endothelial cells and mouse podocytes, and adriamycin-induced transendothelial albumin passage was reduced as well. Importantly, we demonstrated a regulatory effect of PPARɣ on HPSE promoter activity and direct PPARy binding to the HPSE promoter region. Plasma HPSE activity of T2DM patients treated with pioglitazone for 16/24 weeks was related to their hemoglobin A1c and showed a moderate, near significant correlation with plasma creatinine levels.

INTERPRETATION

PPARɣ-mediated regulation of HPSE expression appears an additional mechanism explaining the anti-proteinuric and renoprotective effects of thiazolidinediones in clinical practice.

FUNDING

This study was financially supported by the Dutch Kidney Foundation, by grants 15OI36, 13OKS023 and 15OP13. Consortium grant LSHM16058-SGF (GLYCOTREAT; a collaboration project financed by the PPP allowance made available by Top Sector Life Sciences & Health to the Dutch Kidney Foundation to stimulate public-private partnerships).

Integrative methylome and transcriptome analysis of porcine abdominal fat indicates changes in fat metabolism and immune responses during different development

Fat is involved in synthesizing fatty acids (FAs), FA circulation, and lipid metabolism. Various genetic studies have been conducted on porcine fat but understanding the growth and specific adipose tissue is insufficient. The purpose of this study is to investigate the epigenetic difference in abdominal fat according to the growth of porcine. The samples were collected from the porcine abdominal fat of different developmental stages (10 and 26 weeks of age). Then, the samples were sequenced using MBD-seq and RNA-seq for profiling DNA methylation and RNA expression. In 26 weeks of age pigs, differentially methylated genes (DMGs) and differentially expressed genes (DEGs) were identified as 2,251 and 5,768, compared with 10 weeks of age pigs, respectively. Gene functional analysis was performed using GO and KEGG databases. In functional analysis results of DMGs and DEGs, immune responses such as chemokine signaling pathways, B cell receptor signaling pathways, and lipid metabolism terms such as PPAR signaling pathways and fatty acid degradation were identified. It is thought that there is an influence between DNA methylation and gene expression through changes in genes with similar functions. The effects of DNA methylation on gene expression were investigated using cis-regulation and trans-regulation analysis to integrate and interpret different molecular layers. In the cis-regulation analysis using 629 overlapping genes between DEGs and DMGs, immune response functions were identified, while in trans-regulation analysis through the TF-target gene network, the co-expression network of lipid metabolism-related functions was distinguished. Our research provides an understanding of the underlying mechanisms for epigenetic regulation in porcine abdominal fat with aging.

Lipedema: Insights into Morphology, Pathophysiology, and Challenges

Lipedema is an adipofascial disorder that almost exclusively affects women. Lipedema leads to chronic pain, swelling, and other discomforts due to the bilateral and asymmetrical expansion of subcutaneous adipose tissue. Although various distinctive morphological characteristics, such as the hyperproliferation of fat cells, fibrosis, and inflammation, have been characterized in the progression of lipedema, the mechanisms underlying these changes have not yet been fully investigated. In addition, it is challenging to reduce the excessive fat in lipedema patients using conventional weight-loss techniques, such as lifestyle (diet and exercise) changes, bariatric surgery, and pharmacological interventions. Therefore, lipedema patients also go through additional psychosocial distress in the absence of permanent treatment. Research to understand the pathology of lipedema is still in its infancy, but promising markers derived from exosome, cytokine, lipidomic, and metabolomic profiling studies suggest a condition distinct from obesity and lymphedema. Although genetics seems to be a substantial cause of lipedema, due to the small number of patients involved in such studies, the extrapolation of data at a broader scale is challenging. With the current lack of etiology-guided treatments for lipedema, the discovery of new promising biomarkers could provide potential solutions to combat this complex disease. This review aims to address the morphological phenotype of lipedema fat, as well as its unclear pathophysiology, with a primary emphasis on excessive interstitial fluid, extracellular matrix remodeling, and lymphatic and vasculature dysfunction. The potential mechanisms, genetic implications, and proposed biomarkers for lipedema are further discussed in detail. Finally, we mention the challenges related to lipedema and emphasize the prospects of technological interventions to benefit the lipedema community in the future.

PPAR-γ Partial Agonists in Disease-Fate Decision with Special Reference to Cancer

Peroxisome proliferator-activated receptor-γ (PPAR-γ) has emerged as one of the most extensively studied transcription factors since its discovery in 1990, highlighting its importance in the etiology and treatment of numerous diseases involving various types of cancer, type 2 diabetes mellitus, autoimmune, dermatological and cardiovascular disorders. Ligands are regarded as the key determinant for the tissue-specific activation of PPAR-γ. However, the mechanism governing this process is merely a contradictory debate which is yet to be systematically researched. Either these receptors get weakly activated by endogenous or natural ligands or leads to a direct over-activation process by synthetic ligands, serving as complete full agonists. Therefore, fine-tuning on the action of PPAR-γ and more subtle modulation can be a rewarding approach which might open new avenues for the treatment of several diseases. In the recent era, researchers have sought to develop safer partial PPAR-γ agonists in order to dodge the toxicity induced by full agonists, akin to a balanced activation. With a particular reference to cancer, this review concentrates on the therapeutic role of partial agonists, especially in cancer treatment. Additionally, a timely examination of their efficacy on various other disease-fate decisions has been also discussed.

Role of Transcription Factors in the Management of Preterm Birth: Impact on Future Treatment Strategies

Preterm birth is defined as the birth of a neonate before 37 weeks of gestation and is considered as a leading cause of the under five deaths of neonates. Neonates born preterm are known to have higher perinatal mortality and morbidity with associated risks of low birth weight, respiratory distress syndrome, gastrointestinal, immunologic, central nervous system, hearing, and vision problems, cerebral palsy, and delayed development. India leads the list of countries with the greatest number of preterm births. The studies focusing on the molecular mechanisms related to the etiology of preterm birth have described the role of different transcription factors. With respect to this, transcription factors like peroxisome proliferator activated receptors (PPAR), nuclear factor kappa β (NF-kβ), nuclear erythroid 2-related factor 2 (Nrf2), and progesterone receptor (PR) are known to be associated with preterm labor. All these transcription factors are linked together with a common cascade involving inflammatory processes. Thus, the current review describes the possible cross-talk between these transcription factors and their therapeutic potential to prevent or manage preterm labor.

Balanced control of thermogenesis by nuclear receptor corepressors in brown adipose tissue

Brown adipose tissue (BAT) is a key thermogenic organ whose expression of uncoupling protein 1 (UCP1) and ability to maintain body temperature in response to acute cold exposure require histone deacetylase 3 (HDAC3). HDAC3 exists in tight association with nuclear receptor corepressors (NCoRs) NCoR1 and NCoR2 (also known as silencing mediator of retinoid and thyroid receptors [SMRT]), but the functions of NCoR1/2 in BAT have not been established. Here we report that as expected, genetic loss of NCoR1/2 in BAT (NCoR1/2 BAT-dKO) leads to loss of HDAC3 activity. In addition, HDAC3 is no longer bound at its physiological genomic sites in the absence of NCoR1/2, leading to a shared deregulation of BAT lipid metabolism between NCoR1/2 BAT-dKO and HDAC3 BAT-KO mice. Despite these commonalities, loss of NCoR1/2 in BAT does not phenocopy the cold sensitivity observed in HDAC3 BAT-KO, nor does loss of either corepressor alone. Instead, BAT lacking NCoR1/2 is inflamed, particularly with respect to the interleukin-17 axis that increases thermogenic capacity by enhancing innervation. Integration of BAT RNA sequencing and chromatin immunoprecipitation sequencing data revealed that NCoR1/2 directly regulate Mmp9, which integrates extracellular matrix remodeling and inflammation. These findings reveal pleiotropic functions of the NCoR/HDAC3 corepressor complex in BAT, such that HDAC3-independent suppression of BAT inflammation counterbalances stimulation of HDAC3 activity in the control of thermogenesis.

Arylalkynyl amide-type peroxisome proliferator-activated receptor γ (PPARγ)-selective antagonists covalently bind to the PPARγ ligand binding domain with a unique binding mode

Peroxisome proliferator-activated receptor γ (PPARγ) antagonists are drug candidates for the treatment of type 2 diabetes, obesity, and osteoporosis. Previously, we have designed and synthesized a series of substituted phenylalkynyl amide-type PPARγ antagonists. The representative compound, MMT-160, exhibited nanomolar-order PPARγ antagonistic activity. To understand the antagonistic mode of action of MMT-160, mass spectrometric and X-ray crystallographic analysis of MMT-160 in the presence of the PPARγ ligand binding domain (LBD) were performed. The mass spectrometry results clearly indicated that alkynyl amide-type PPARγ antagonists were covalently bound to the PPARγ LBD. The X-ray crystallographic analysis indicated that MMT-160 acted as a Michael acceptor and covalently bound to the PPARγ LBD via Cys285. In addition, MMT-160 bound to the PPARγ LBD with a binding mode that was different from the binding modes observed for PPARγ agonists and partial agonists.

Elucidating the Novel Mechanism of Ligustrazine in Preventing Postoperative Peritoneal Adhesion Formation

Postoperative peritoneal adhesion (PPA) is a major clinical complication after open surgery or laparoscopic procedure. Ligustrazine is the active ingredient extracted from the natural herb Ligusticum chuanxiong Hort, which has promising antiadhesion properties. This study is aimed at revealing the underlying mechanisms of ligustrazine in preventing PPA at molecular and cellular levels. Both rat primary peritoneal mesothelial cells (PMCs) and human PMCs were used for analysis in vitro. Several molecular biological techniques were applied to uncover the potential mechanisms of ligustrazine in preventing PPA. And molecular docking and site-directed mutagenesis assay were used to predict the binding sites of ligustrazine with PPARγ. The bioinformatics analysis was further applied to identify the key pathway in the pathogenesis of PPA. Besides, PPA rodent models were prepared and developed to evaluate the novel ligustrazine nanoparticles in vivo. Ligustrazine could significantly suppress hypoxia-induced PMC functions, such as restricting the production of profibrotic cytokines, inhibiting the expression of migration and adhesion-associated molecules, repressing the expression of cytoskeleton proteins, restricting hypoxia-induced PMCs to obtain myofibroblast-like phenotypes, and reversing ECM remodeling and EMT phenotype transitions by activating PPARγ. The antagonist GW9662 of PPARγ could restore the inhibitory effects of ligustrazine on hypoxia-induced PMC functions. The inhibitor KC7F2 of HIF-1α could repress hypoxia-induced PMC functions, and ligustrazine could downregulate the expression of HIF-1α, which could be reversed by GW9662. And the expression of HIF-1α inhibited by ligustrazine was dramatically reversed after transfection with si-SMRT. The results showed that the benefit of ligustrazine on PMC functions is contributed to the activation of PPARγ on the transrepression of HIF-1α in an SMRT-dependent manner. Molecular docking and site-directed mutagenesis tests uncovered that ligustrazine bound directly to PPARγ, and Val 339/Ile 341 residue was critical for the binding of PPARγ to ligustrazine. Besides, we discovered a novel nanoparticle agent with sustained release behavior, drug delivery efficiency, and good tissue penetration in PPA rodent models. Our study unravels a novel mechanism of ligustrazine in preventing PPA. The findings indicated that ligustrazine is a potential strategy for PPA formation and ligustrazine nanoparticles are promising agents for preclinical application.

Physiological Convergence and Antagonism Between GR and PPARγ in Inflammation and Metabolism

Nuclear receptors (NRs) are transcription factors that modulate gene expression in a ligand-dependent manner. The ubiquitously expressed glucocorticoid receptor (GR) and peroxisome proliferator-activated receptor gamma (PPARγ) represent steroid (type I) and non-steroid (type II) classes of NRs, respectively. The diverse transcriptional and physiological outcomes of their activation are highly tissue-specific. For example, in subsets of immune cells, such as macrophages, the signaling of GR and PPARγ converges to elicit an anti-inflammatory phenotype; in contrast, in the adipose tissue, their signaling can lead to reciprocal metabolic outcomes. This review explores the cooperative and divergent outcomes of GR and PPARγ functions in different cell types and tissues, including immune cells, adipose tissue and the liver. Understanding the coordinated control of these NR pathways should advance studies in the field and potentially pave the way for developing new therapeutic approaches to exploit the GR:PPARγ crosstalk.

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.

Regulatory roles and mechanisms of alternative RNA splicing in adipogenesis and human metabolic health

Alternative splicing (AS) regulates gene expression patterns at the post-transcriptional level and generates a striking expansion of coding capacities of genomes and cellular protein diversity. RNA splicing could undergo modulation and close interaction with genetic and epigenetic machinery. Notably, during the adipogenesis processes of white, brown and beige adipocytes, AS tightly interplays with the differentiation gene program networks. Here, we integrate the available findings on specific splicing events and distinct functions of different splicing regulators as examples to highlight the directive biological contribution of AS mechanism in adipogenesis and adipocyte biology. Furthermore, accumulating evidence has suggested that mutations and/or altered expression in splicing regulators and aberrant splicing alterations in the obesity-associated genes are often linked to humans’ diet-induced obesity and metabolic dysregulation phenotypes. Therefore, significant attempts have been finally made to overview novel detailed discussion on the prospects of splicing machinery with obesity and metabolic disorders to supply featured potential management mechanisms in clinical applicability for obesity treatment strategies.

SIAH2 is Expressed in Adipocyte Precursor Cells and Interacts with EBF1 and ZFP521 to Promote Adipogenesis

OBJECTIVE

Expression of zinc finger protein 423 (ZFP423), a key proadipogenic transcription factor in adipocyte precursor cells, is regulated by interaction of the proadipogenic early B-cell factor 1 (EBF1) and antiadipogenic ZFP521. The ubiquitin ligase seven-in-absentia homolog 2 (SIAH2) targets ZFP521 for degradation. This study asked whether SIAH2 is expressed in adipocyte precursor cells and whether SIAH2 interacts with ZFP521 and EBF1 to regulate ZFP521 protein levels during adipogenesis.

METHODS

SIAH2 expression in precursor cells was assessed in primary cells and tissues from wild-type and SIAH2 null mice fed a control or high-fat diet. Primary cells, 3T3-L1 preadipocytes, and HEK293T cells were used to analyze Siah2, Ebf1, and Zfp521 expression and SIAH2-mediated changes in ZFP521 and EBF1 protein levels.

RESULTS

Siah2 is expressed in platelet-derived growth factor receptor α (PDGFRα)⁺ and stem cell antigen-1 (SCA1)⁺ adipocyte precursor cells. SIAH2 depletion reduces Ebf1 gene expression and increases EBF1 protein levels in early but not late adipogenesis. In early adipogenesis, SIAH2 forms a protein complex with EBF1 and ZFP521 to enhance SIAH2-mediated ubiquitylation and degradation of ZFP521 while increasing EBF1 protein levels.

CONCLUSIONS

Siah2 is expressed in PDGFRα+ adipocyte precursor cells and is linked to precursor cell commitment to adipogenesis by interacting with EBF1 and ZFP521 proteins to target the antiadipogenic ZFP521 for degradation.

PPARγ S273 Phosphorylation Modifies the Dynamics of Coregulator Proteins Recruitment

The nuclear receptor PPARγ is essential to maintain whole-body glucose homeostasis and insulin sensitivity, acting as a master regulator of adipogenesis, lipid, and glucose metabolism. Its activation through natural or synthetic ligands induces the recruitment of coactivators, leading to transcription of target genes such as cytokines and hormones. More recently, post translational modifications, such as PPARγ phosphorylation at Ser273 by CDK5 in adipose tissue, have been linked to insulin resistance trough the dysregulation of expression of a specific subset of genes. Here, we investigate how this phosphorylation may disturb the interaction between PPARγ and some coregulator proteins as a new mechanism that may leads to insulin resistance. Through cellular and in vitro assays, we show that PPARγ phosphorylation inhibition increased the activation of the receptor, therefore the increased recruitment of PGC1-α and TIF2 coactivators, whilst decreases the interaction with SMRT and NCoR corepressors. Moreover, our results show a shift in the coregulators interaction domains preferences, suggesting additional interaction interfaces formed between the phosphorylated PPARγ and some coregulator proteins. Also, we observed that the CDK5 presence disturb the PPARγ-coregulator's synergy, decreasing interaction with PGC1-α, TIF2, and NCoR, but increasing coupling of SMRT. Finally, we conclude that the insulin resistance provoked by PPARγ phosphorylation is linked to a differential coregulators recruitment, which may promote dysregulation in gene expression.

Peroxisome Proliferator-Activated Receptors as Molecular Links between Caloric Restriction and Circadian Rhythm

The circadian rhythm plays a chief role in the adaptation of all bodily processes to internal and environmental changes on the daily basis. Next to light/dark phases, feeding patterns constitute the most essential element entraining daily oscillations, and therefore, timely and appropriate restrictive diets have a great capacity to restore the circadian rhythm. One of the restrictive nutritional approaches, caloric restriction (CR) achieves stunning results in extending health span and life span via coordinated changes in multiple biological functions from the molecular, cellular, to the whole-body levels. The main molecular pathways affected by CR include mTOR, insulin signaling, AMPK, and sirtuins. Members of the family of nuclear receptors, the three peroxisome proliferator-activated receptors (PPARs), PPARα, PPARβ/δ, and PPARγ take part in the modulation of these pathways. In this non-systematic review, we describe the molecular interconnection between circadian rhythm, CR-associated pathways, and PPARs. Further, we identify a link between circadian rhythm and the outcomes of CR on the whole-body level including oxidative stress, inflammation, and aging. Since PPARs contribute to many changes triggered by CR, we discuss the potential involvement of PPARs in bridging CR and circadian rhythm.

SMRT Regulates Metabolic Homeostasis and Adipose Tissue Macrophage Phenotypes in Tandem

The Silencing Mediator of Retinoid and Thyroid Hormone Receptors (SMRT) is a nuclear corepressor, regulating the transcriptional activity of many transcription factors critical for metabolic processes. While the importance of the role of SMRT in the adipocyte has been well-established, our comprehensive understanding of its in vivo function in the context of homeostatic maintenance is limited due to contradictory phenotypes yielded by prior generalized knockout mouse models. Multiple such models agree that SMRT deficiency leads to increased adiposity, although the effects of SMRT loss on glucose tolerance and insulin sensitivity have been variable. We therefore generated an adipocyte-specific SMRT knockout (adSMRT-/-) mouse to more clearly define the metabolic contributions of SMRT. In doing so, we found that SMRT deletion in the adipocyte does not cause obesity-even when mice are challenged with a high-fat diet. This suggests that adiposity phenotypes of previously described models were due to effects of SMRT loss beyond the adipocyte. However, an adipocyte-specific SMRT deficiency still led to dramatic effects on systemic glucose tolerance and adipocyte insulin sensitivity, impairing both. This metabolically deleterious outcome was coupled with a surprising immune phenotype, wherein most genes differentially expressed in the adipose tissue of adSMRT-/- mice were upregulated in pro-inflammatory pathways. Flow cytometry and conditioned media experiments demonstrated that secreted factors from knockout adipose tissue strongly informed resident macrophages to develop a pro-inflammatory, MMe (metabolically activated) phenotype. Together, these studies suggest a novel role for SMRT as an integrator of metabolic and inflammatory signals to maintain physiological homeostasis.

Gestational exposures to organophosphorus insecticides: From acute poisoning to developmental neurotoxicity

For over three-quarters of a century, organophosphorus (OP) insecticides have been ubiquitously used in agricultural, residential, and commercial settings and in public health programs to mitigate insect-borne diseases. Their broad-spectrum insecticidal effectiveness is accounted for by the irreversible inhibition of acetylcholinesterase (AChE), the enzyme that catalyzes acetylcholine (ACh) hydrolysis, in the nervous system of insects. However, because AChE is evolutionarily conserved, OP insecticides are also toxic to mammals, including humans, and acute OP intoxication remains a major public health concern in countries where OP insecticide usage is poorly regulated. Environmental exposures to OP levels that are generally too low to cause marked inhibition of AChE and to trigger acute signs of intoxication, on the other hand, represent an insidious public health issue worldwide. Gestational exposures to OP insecticides are particularly concerning because of the exquisite sensitivity of the developing brain to these insecticides. The present article overviews and discusses: (i) the health effects and therapeutic management of acute OP poisoning during pregnancy, (ii) epidemiological studies examining associations between environmental OP exposures during gestation and health outcomes of offspring, (iii) preclinical evidence that OP insecticides are developmental neurotoxicants, and (iv) potential mechanisms underlying the developmental neurotoxicity of OP insecticides. Understanding how gestational exposures to different levels of OP insecticides affect pregnancy and childhood development is critical to guiding implementation of preventive measures and direct research aimed at identifying effective therapeutic interventions that can limit the negative impact of these exposures on public health.

Loss of G protein pathway suppressor 2 in human adipocytes triggers lipid remodeling by upregulating ATP binding cassette subfamily G member 1

OBJECTIVE

Adipogenesis is critical for adipose tissue remodeling during the development of obesity. While the role of transcription factors in the orchestration of adipogenic pathways is already established, the involvement of coregulators that transduce regulatory signals into epigenome alterations and transcriptional responses remains poorly understood. The aim of our study was to investigate which pathways are controlled by G protein pathway suppressor 2 (GPS2) during the differentiation of human adipocytes.

METHODS

We generated a unique loss-of-function model by RNAi depletion of GPS2 in human multipotent adipose-derived stem (hMADS) cells. We thoroughly characterized the coregulator depletion-dependent pathway alterations during adipocyte differentiation at the level of transcriptome (RNA-seq), epigenome (ChIP-seq H3K27ac), cistrome (ChIP-seq GPS2), and lipidome. We validated the in vivo relevance of the identified pathways in non-diabetic and diabetic obese patients.

RESULTS

The loss of GPS2 triggers the reprogramming of cellular processes related to adipocyte differentiation by increasing the responses to the adipogenic cocktail. In particular, GPS2 depletion increases the expression of BMP4, an important trigger for the commitment of fibroblast-like progenitors toward the adipogenic lineage and increases the expression of inflammatory and metabolic genes. GPS2-depleted human adipocytes are characterized by hypertrophy, triglyceride and phospholipid accumulation, and sphingomyelin depletion. These changes are likely a consequence of the increased expression of ATP-binding cassette subfamily G member 1 (ABCG1) that mediates sphingomyelin efflux from adipocytes and modulates lipoprotein lipase (LPL) activity. We identify ABCG1 as a direct transcriptional target, as GPS2 depletion leads to coordinated changes of transcription and H3K27 acetylation at promoters and enhancers that are occupied by GPS2 in wild-type adipocytes. We find that in omental adipose tissue of obese humans, GPS2 levels correlate with ABCG1 levels, type 2 diabetic status, and lipid metabolic status, supporting the in vivo relevance of the hMADS cell-derived in vitro data.

CONCLUSION

Our study reveals a dual regulatory role of GPS2 in epigenetically modulating the chromatin landscape and gene expression during human adipocyte differentiation and identifies a hitherto unknown GPS2-ABCG1 pathway potentially linked to adipocyte hypertrophy in humans.

Peroxisome Proliferator-Activated Receptors and Caloric Restriction-Common Pathways Affecting Metabolism, Health, and Longevity

Caloric restriction (CR) is a traditional but scientifically verified approach to promoting health and increasing lifespan. CR exerts its effects through multiple molecular pathways that trigger major metabolic adaptations. It influences key nutrient and energy-sensing pathways including mammalian target of rapamycin, Sirtuin 1, AMP-activated protein kinase, and insulin signaling, ultimately resulting in reductions in basic metabolic rate, inflammation, and oxidative stress, as well as increased autophagy and mitochondrial efficiency. CR shares multiple overlapping pathways with peroxisome proliferator-activated receptors (PPARs), particularly in energy metabolism and inflammation. Consequently, several lines of evidence suggest that PPARs might be indispensable for beneficial outcomes related to CR. In this review, we present the available evidence for the interconnection between CR and PPARs, highlighting their shared pathways and analyzing their interaction. We also discuss the possible contributions of PPARs to the effects of CR on whole organism outcomes.

Positive Reinforcing Mechanisms between GPR120 and PPARγ Modulate Insulin Sensitivity

G protein-coupled receptor 120 (GPR120) and PPARγ agonists each have insulin sensitizing effects. But whether these two pathways functionally interact and can be leveraged together to markedly improve insulin resistance has not been explored. Here, we show that treatment with the PPARγ agonist rosiglitazone (Rosi) plus the GPR120 agonist Compound A leads to additive effects to improve glucose tolerance and insulin sensitivity, but at lower doses of Rosi, thus avoiding its known side effects. Mechanistically, we show that GPR120 is a PPARγ target gene in adipocytes, while GPR120 augments PPARγ activity by inducing the endogenous ligand 15d-PGJ2 and by blocking ERK-mediated inhibition of PPARγ. Further, we used macrophage- (MKO) or adipocyte-specific GPR120 KO (AKO) mice to show that GRP120 has anti-inflammatory effects via macrophages while working with PPARγ in adipocytes to increase insulin sensitivity. These results raise the prospect of a safer way to increase insulin sensitization in the clinic.

A molecular switch regulating transcriptional repression and activation of PPARγ

Nuclear receptor (NR) transcription factors use a conserved activation function-2 (AF-2) helix 12 mechanism for agonist-induced coactivator interaction and NR transcriptional activation. In contrast, ligand-induced corepressor-dependent NR repression appears to occur through structurally diverse mechanisms. We report two crystal structures of peroxisome proliferator-activated receptor gamma (PPARγ) in an inverse agonist/corepressor-bound transcriptionally repressive conformation. Helix 12 is displaced from the solvent-exposed active conformation and occupies the orthosteric ligand-binding pocket enabled by a conformational change that doubles the pocket volume. Paramagnetic relaxation enhancement (PRE) NMR and chemical crosslinking mass spectrometry confirm the repressive helix 12 conformation. PRE NMR also defines the mechanism of action of the corepressor-selective inverse agonist T0070907, and reveals that apo-helix 12 exchanges between transcriptionally active and repressive conformations—supporting a fundamental hypothesis in the NR field that helix 12 exchanges between transcriptionally active and repressive conformations.

Structural studies of nuclear receptor transcription factors revealed that nearly all nuclear receptors share a conserved helix 12 dependent transcriptional activation mechanism. Here the authors present two crystal structures of peroxisome proliferator-activated receptor gamma (PPARγ) in an inverse agonist/corepressor-bound transcriptionally repressive conformation, where helix 12 is located within the orthosteric ligand-binding pocket instead, and discuss mechanistic implications.

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.

Collaborative Regulation of LRG1 by TGF-β1 and PPAR-β/δ Modulates Chronic Pressure Overload-Induced Cardiac Fibrosis

BACKGROUND

Despite its established significance in fibrotic cardiac remodeling, clinical benefits of global inhibition of TGF (transforming growth factor)-β1 signaling remain controversial. LRG1 (leucine-rich-α2 glycoprotein 1) is known to regulate endothelial TGFβ signaling. This study evaluated the role of LRG1 in cardiac fibrosis and its transcriptional regulatory network in cardiac fibroblasts.

METHODS

Pressure overload-induced heart failure was established by transverse aortic constriction. Western blot, quantitative reverse transcription polymerase chain reaction, immunofluorescence, and immunohistochemistry were used to evaluate the expression level and pattern of interested targets or pathology during fibrotic cardiac remodeling. Cardiac function was assessed by pressure-volume loop analysis.

RESULTS

LRG1 expression was significantly suppressed in left ventricle of mice with transverse aortic constriction-induced fibrotic cardiac remodeling (mean difference, -0.00085 [95% CI, -0.0013 to -0.00043]; P=0.005) and of patients with end-stage ischemic-dilated cardiomyopathy (mean difference, 0.13 [95% CI, 0.012-0.25]; P=0.032). More profound cardiac fibrosis (mean difference, -0.014% [95% CI, -0.029% to -0.00012%]; P=0.048 for interstitial fibrosis; mean difference, -1.3 [95% CI, -2.5 to -0.2]; P=0.016 for perivascular fibrosis), worse cardiac dysfunction (mean difference, -2.5 ms [95% CI, -4.5 to -0.4 ms]; P=0.016 for Tau-g; mean difference, 13% [95% CI, 2%-24%]; P=0.016 for ejection fraction), and hyperactive TGFβ signaling in transverse aortic constriction-operated Lrg1-deficient mice (mean difference, -0.27 [95% CI, -0.47 to -0.07]; P<0.001), which could be reversed by cardiac-specific Lrg1 delivery mediated by adeno-associated virus 9. Mechanistically, LRG1 inhibits cardiac fibroblast activation by competing with TGFβ1 for receptor binding, while PPAR (peroxisome proliferator-activated receptor)-β/δ and TGFβ1 collaboratively regulate LRG1 expression via SMRT (silencing mediator for retinoid and thyroid hormone receptor). We further demonstrated functional interactions between LRG1 and PPARβ/δ in cardiac fibroblast activation.

CONCLUSIONS

Our results established a highly complex molecular network involving LRG1, TGFβ1, PPARβ/δ, and SMRT in regulating cardiac fibroblast activation and cardiac fibrosis. Targeting LRG1 or PPARβ/δ represents a promising strategy to control pathological cardiac remodeling in response to chronic pressure overload.

PPARβ/δ recruits NCOR and regulates transcription reinitiation of ANGPTL4

In the absence of ligands, the nuclear receptor PPARβ/δ recruits the NCOR and SMRT corepressors, which form complexes with HDAC3, to canonical target genes. Agonistic ligands cause dissociation of corepressors and enable enhanced transcription. Vice versa, synthetic inverse agonists augment corepressor recruitment and repression. Both basal repression of the target gene ANGPTL4 and reinforced repression elicited by inverse agonists are partially insensitive to HDAC inhibition. This raises the question how PPARβ/δ represses transcription mechanistically. We show that the PPARβ/δ inverse agonist PT-S264 impairs transcription initiation by decreasing recruitment of activating Mediator subunits, RNA polymerase II, and TFIIB, but not of TFIIA, to the ANGPTL4 promoter. Mass spectrometry identifies NCOR as the main PT-S264-dependent interactor of PPARβ/δ. Reconstitution of knockout cells with PPARβ/δ mutants deficient in basal repression results in diminished recruitment of NCOR, SMRT, and HDAC3 to PPAR target genes, while occupancy by RNA polymerase II is increased. PT-S264 restores binding of NCOR, SMRT, and HDAC3 to the mutants, resulting in reduced polymerase II occupancy. Our findings corroborate deacetylase-dependent and -independent repressive functions of HDAC3-containing complexes, which act in parallel to downregulate transcription.

Gene Expression Profiles Controlled by the Alternative Splicing Factor Nova2 in Endothelial Cells

Alternative splicing (AS) plays an important role in expanding the complexity of the human genome through the production of specialized proteins regulating organ development and physiological functions, as well as contributing to several pathological conditions. How AS programs impact on the signaling pathways controlling endothelial cell (EC) functions and vascular development is largely unknown. Here we identified, through RNA-seq, changes in mRNA steady-state levels in ECs caused by the neuro-oncological ventral antigen 2 (Nova2), a key AS regulator of the vascular morphogenesis. Bioinformatics analyses identified significant enrichment for genes regulated by peroxisome proliferator-activated receptor-gamma (Ppar-γ) and E2F1 transcription factors. We also showed that Nova2 in ECs controlled the AS profiles of Ppar-γ and E2F dimerization partner 2 (Tfdp2), thus generating different protein isoforms with distinct function (Ppar-γ) or subcellular localization (Tfdp2). Collectively, our results supported a mechanism whereby Nova2 integrated splicing decisions in order to regulate Ppar-γ and E2F1 activities. Our data added a layer to the sequential series of events controlled by Nova2 in ECs to orchestrate vascular biology.

Deletion of intestinal Hdac3 remodels the lipidome of enterocytes and protects mice from diet-induced obesity

Histone deacetylase 3 (Hdac3) regulates the expression of lipid metabolism genes in multiple tissues, however its role in regulating lipid metabolism in the intestinal epithelium is unknown. Here we demonstrate that intestine-specific deletion of Hdac3 (Hdac3^IKO) protects mice from diet induced obesity. Intestinal epithelial cells (IECs) from Hdac3^IKO mice display co-ordinate induction of genes and proteins involved in mitochondrial and peroxisomal β-oxidation, have an increased rate of fatty acid oxidation, and undergo marked remodelling of their lipidome, particularly a reduction in long chain triglycerides. Many HDAC3-regulated fatty oxidation genes are transcriptional targets of the PPAR family of nuclear receptors, Hdac3 deletion enhances their induction by PPAR-agonists, and pharmacological HDAC3 inhibition induces their expression in enterocytes. These findings establish a central role for HDAC3 in co-ordinating PPAR-regulated lipid oxidation in the intestinal epithelium, and identify intestinal HDAC3 as a potential therapeutic target for preventing obesity and related diseases.

Histone deacetylase 3 (HDAC3) is a regulator of lipid homeostasis in several tissues, however, its role in intestinal lipid metabolism was not yet known. Here the authors study intestine specific HDAC3 knock out mice and report that these animals have increased fatty acid oxidation and undergo remodeling of the intestinal epithelial cell lipidome.

NCoR1: Putting the Brakes on the Dendritic Cell Immune Tolerance

Understanding the mechanisms fine-tuning immunogenic versus tolerogenic balance in dendritic cells (DCs) is of high importance for therapeutic approaches. We found that NCoR1-mediated direct repression of the tolerogenic program in conventional DCs is essential for induction of an optimal immunogenic response. NCoR1 depletion upregulated a wide variety of tolerogenic genes in activated DCs, which consequently resulted in increased frequency of FoxP3⁺ regulatory T cells. Mechanistically, NCoR1 masks the PU.1-bound super-enhancers on major tolerogenic genes after DC activation that are subsequently bound by nuclear factor-κB. NCoR1 knockdown (KD) reduced RelA nuclear translocation and activity, whereas RelB was unaffected, providing activated DCs a tolerogenic advantage. Moreover, NCoR1^DC−/- mice depicted enhanced Tregs in draining lymph nodes with increased disease burden upon bacterial and parasitic infections. Besides, adoptive transfer of activated NCoR1 KD DCs in infected animals showed a similar phenotype. Collectively, our results demonstrated NCoR1 as a promising target to control DC-mediated immune tolerance.

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NCoR1 directly represses tolerogenic program in mouse cDCs

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Depletion of NCoR1 in cDCs enhanced Treg development ex vivo and in vivo

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NCoR1 masks PU.1-bound super-enhancers on tolerogenic genes in cDCs

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NCoR1^DC−/− animals depicted enhanced Treg frequency and infection load

Prenatal androgen excess alters the uterine peroxisome proliferator-activated receptor (PPAR) system

It is known that androgen excess induces changes in fetal programming that affect several physiological pathways. Peroxisome proliferator-activated receptors (PPARs) α, δ and γ are key mediators of female reproductive functions, in particular in uterine tissues. Thus, we aimed to study the effect of prenatal hyperandrogenisation on the uterine PPAR system. Rats were treated with 2mg testosterone from Day 16 to 19 of pregnancy. Female offspring (PH group) were followed until 90 days of life, when they were killed. The PH group exhibited an anovulatory phenotype. We quantified uterine mRNA levels of PPARα (Ppara ), PPARδ (Ppard ), PPARγ (Pparg ), their regulators peroxisome proliferator-activated receptor gamma coactivator 1-alpha (Ppargc1a ) and nuclear receptor co-repressor 1 (Ncor1 ) and cyclo-oxygenase (COX)-2 (Ptgs2 ), and assessed the lipid peroxidation (LP) index and levels of glutathione (GSH) and prostaglandin (PG) E2 . The PH group showed decreased levels of all uterine PPAR isoforms compared with the control group. In addition, PGE2 and Ptgs2 levels were increased in the PH group, which led to a uterine proinflammatory environment, as was LP, which led to a pro-oxidant status that GSH was not able to compensate for. These results suggest that prenatal exposure to androgen excess has a fetal programming effect that affects the gene expression of PPAR isoforms, and creates a misbalanced oxidant-antioxidant state and a proinflammatory status.

Hepatocyte-specific loss of GPS2 in mice reduces non-alcoholic steatohepatitis via activation of PPARα

Obesity triggers the development of non-alcoholic fatty liver disease (NAFLD), which involves alterations of regulatory transcription networks and epigenomes in hepatocytes. Here we demonstrate that G protein pathway suppressor 2 (GPS2), a subunit of the nuclear receptor corepressor (NCOR) and histone deacetylase 3 (HDAC3) complex, has a central role in these alterations and accelerates the progression of NAFLD towards non-alcoholic steatohepatitis (NASH). Hepatocyte-specific Gps2 knockout in mice alleviates the development of diet-induced steatosis and fibrosis and causes activation of lipid catabolic genes. Integrative cistrome, epigenome and transcriptome analysis identifies the lipid-sensing peroxisome proliferator-activated receptor α (PPARα, NR1C1) as a direct GPS2 target. Liver gene expression data from human patients reveal that Gps2 expression positively correlates with a NASH/fibrosis gene signature. Collectively, our data suggest that the GPS2-PPARα partnership in hepatocytes coordinates the progression of NAFLD in mice and in humans and thus might be of therapeutic interest.

Self-regulation of the inflammatory response by peroxisome proliferator-activated receptors

The peroxisome proliferator-activated receptor (PPAR) family includes three transcription factors: PPARα, PPARβ/δ, and PPARγ. PPAR are nuclear receptors activated by oxidised and nitrated fatty acid derivatives as well as by cyclopentenone prostaglandins (PGA₂ and 15d-PGJ₂) during the inflammatory response. This results in the modulation of the pro-inflammatory response, preventing it from being excessively activated. Other activators of these receptors are nonsteroidal anti-inflammatory drug (NSAID) and fatty acids, especially polyunsaturated fatty acid (PUFA) (arachidonic acid, ALA, EPA, and DHA). The main function of PPAR during the inflammatory reaction is to promote the inactivation of NF-κB. Possible mechanisms of inactivation include direct binding and thus inactivation of p65 NF-κB or ubiquitination leading to proteolytic degradation of p65 NF-κB. PPAR also exert indirect effects on NF-κB. They promote the expression of antioxidant enzymes, such as catalase, superoxide dismutase, or heme oxygenase-1, resulting in a reduction in the concentration of reactive oxygen species (ROS), i.e., secondary transmitters in inflammatory reactions. PPAR also cause an increase in the expression of IκBα, SIRT1, and PTEN, which interferes with the activation and function of NF-κB in inflammatory reactions.

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.

The TEA domain family transcription factor TEAD4 represses murine adipogenesis by recruiting the cofactors VGLL4 and CtBP2 into a transcriptional complex

The Hippo signaling pathway is known to play an important role in multiple physiological processes, including adipogenesis. However, whether the downstream components of the Hippo pathway are involved in adipogenesis remains unknown. Here we demonstrate that the TEA domain family (TEAD) transcription factors are essential for adipogenesis in murine 3T3-L1 preadipocytes. Knockdown of TEAD1-4 stimulated adipogenesis and increased the expression of adipocyte markers in these cells. Interestingly, we found that the TEAD4 knockdown-mediated adipogenesis proceeded in a Yes-associated protein (YAP)/TAZ (Wwtr1)-independent manner and that adipogenesis suppression in WT cells involved formation of a ternary complex comprising TEAD4 and the transcriptional cofactors C-terminal binding protein 2 (CtBP2) and vestigial-like family member 4 (VGLL4). VGLL4 acted as an adaptor protein that enhanced the interaction between TEAD4 and CtBP2, and this TEAD4-VGLL4-CtBP2 ternary complex dynamically existed at the early stage of adipogenesis. Finally, we verified that TEAD4 directly targets the promoters of major adipogenesis transcription factors such as peroxisome proliferator-activated receptor γ (PPARγ) and adiponectin, C1Q, and collagen domain-containing (Adipoq) during adipogenesis. These findings reveal critical insights into the role of the TEAD4-VGLL4-CtBP2 transcriptional repressor complex in suppression of adipogenesis in murine preadipocytes.

Adipocyte-specific Repression of PPAR-gamma by NCoR Contributes to Scleroderma Skin Fibrosis

BACKGROUND

A pivotal role for adipose tissue homeostasis in systemic sclerosis (SSc) skin fibrosis is increasingly recognized. The nuclear receptor PPAR-γ is the master regulator of adipogenesis. Peroxisome proliferator activated receptor-γ (PPAR-γ) has antifibrotic effects by blocking transforming growth factor-β (TGF-β) and is dysregulated in SSc. To unravel the impact of dysregulated PPAR-γ in SSc, we focused on nuclear corepressor (NCoR), which negatively regulates PPAR-γ activity and suppresses adipogenesis.

METHODS

An NCoR-regulated gene signature was measured in the SSc skin transcriptome. Experimental skin fibrosis was examined in mice with adipocyte-specific NCoR ablation.

RESULTS

SSc skin biopsies demonstrated deregulated NCoR signaling. A 43-gene NCoR gene signature showed strong positive correlation with PPAR-γ signaling (R = 0.919, p < 0.0001), whereas negative correlations with TGF-β signaling (R = - 0.796, p < 0.0001) and the modified Rodnan skin score (R = - 0.49, p = 0.004) were found. Mice with adipocyte-specific NCoR ablation demonstrated significant protection from experimental skin fibrosis and inflammation. The protective effects were mediated primarily through endogenous PPAR-γ.

CONCLUSIONS

Our results implicate, for the first time, to our knowledge, deregulated NCoR/PPAR-γ pathways in SSc, and they support a role of adipocyte modulation of skin fibrosis. Pharmacologic restoration of NCoR/PPAR-γ signaling may represent a novel strategy to control skin fibrosis in SSc.

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.

Ligand-activated PPARγ downregulates CXCR4 gene expression through a novel identified PPAR response element and inhibits breast cancer progression

Stromal Derived Factor-1α (SDF-1α) and its cognate receptor CXCR4 play a key role in mediating breast cancer cell invasion and metastasis. Therefore, drugs able to inhibit CXCR4 activation may add critical tools to reduce tumor progression, especially in the most aggressive form of the breast cancer disease. Peroxisome Proliferator-Activated Receptor (PPAR) γ, a member of the nuclear receptor superfamily, has been found to downregulate CXCR4 gene expression in different cancer cells, however the molecular mechanism underlying this effect is not fully understood. Here, we identified a novel PPARγ-mediated mechanism that negatively regulates CXCR4 expression in both epithelial and stromal breast cancer cells. We found that ligand-activated PPARγ downregulated CXCR4 transcriptional activity through the recruitment of the silencing mediator of retinoid and thyroid hormone receptor (SMRT) corepressor onto a newly identified PPAR response element (PPRE) within the CXCR4 promoter in breast cancer cell lines. As a consequence, the PPARγ agonist rosiglitazone (BRL) significantly inhibited cell migration and invasion and this effect was PPARγ-mediated, since it was reversed in the presence of the PPARγ antagonist GW9662. According to the ability of cancer-associated fibroblasts (CAFs), the most abundant component of breast cancer stroma, to secrete high levels of SDF-1α, BRL reduced migratory promoting activities induced by conditioned media (CM) derived from CAFs and affected CXCR4 downstream signaling pathways activated by CAF-CM. In addition, CAFs exposed to BRL showed a decreased expression of CXCR4, a reduced motility and invasion along with a phenotype characterized by an altered morphology. Collectively, our findings provide novel insights into the role of PPARγ in inhibiting breast cancer progression and further highlight the utility of PPARγ ligands for future therapies aimed at targeting both cancer and surrounding stromal cells in breast cancer patients.

Ubiquitin specific protease 19 involved in transcriptional repression of retinoic acid receptor by stabilizing CORO2A

Deubiquitination via deubiquitinating enzymes (DUBs) has been emerged as one of the important post-translational modifications, resulting in the regulation of numerous target proteins. In this study, we screened new protein biomarkers for adipogenesis, and related studies showed that ubiquitin specific protease 19 (USP19) as a DUB is gradually decreased during adipogenesis and it regulates coronin 2A (CORO2A) as one of the components for the nuclear receptor co-repressor (NCoR) complex in some studies. The regulation of CORO2A through the deubiquitinating activity of USP19 affected the transcriptional repression activity of the retinoic acid receptor (RAR), suggesting that USP19 may be involved in the regulation of RAR-mediated adipogenesis.

Lysophospholipid-Related Diseases and PPARγ Signaling Pathway

The nuclear receptor superfamily includes ligand-inducible transcription factors that play diverse roles in cell metabolism and are associated with pathologies such as cardiovascular diseases. Lysophosphatidic acid (LPA) belongs to a family of lipid mediators. LPA and its naturally occurring analogues interact with G protein-coupled receptors on the cell surface and an intracellular nuclear hormone receptor. In addition, several enzymes that utilize LPA as a substrate or generate it as a product are under its regulatory control. Recent studies have demonstrated that the endogenously produced peroxisome proliferator-activated receptor gamma (PPARγ) antagonist cyclic phosphatidic acid (cPA), which is structurally similar to LPA, inhibits cancer cell invasion and metastasis in vitro and in vivo. We recently observed that cPA negatively regulates PPARγ function by stabilizing the binding of the co-repressor protein, a silencing mediator of retinoic acid, and the thyroid hormone receptor. We also showed that cPA prevents neointima formation, adipocyte differentiation, lipid accumulation, and upregulation of PPARγ target gene transcription. The present review discusses the arbitrary aspects of the physiological and pathophysiological actions of lysophospholipids in vascular and nervous system biology.

Ligand-dependent corepressor (LCoR) represses the transcription factor C/EBPβ during early adipocyte differentiation

Nuclear receptors (NRs) regulate gene transcription by recruiting coregulators, involved in chromatin remodeling and assembly of the basal transcription machinery. The NR-associated protein ligand-dependent corepressor (LCoR) has previously been shown to suppress hepatic lipogenesis by decreasing the binding of steroid receptor coactivators to thyroid hormone receptor. However, the role of LCoR in adipogenesis has not been established. Here, we show that LCoR expression is reduced in the early stage of adipogenesis in vitro LCoR overexpression inhibited 3T3-L1 adipocyte differentiation, whereas LCoR knockdown promoted it. Using an unbiased affinity purification approach, we identified CCAAT/enhancer-binding protein β (C/EBPβ), a key transcriptional regulator in early adipogenesis, and corepressor C-terminal binding proteins as potential components of an LCoR-containing complex in 3T3-L1 adipocytes. We found that LCoR directly interacts with C/EBPβ through its C-terminal helix-turn-helix domain, required for LCoR's inhibitory effects on adipogenesis. LCoR overexpression also inhibited C/EBPβ transcriptional activity, leading to inhibition of mitotic clonal expansion and transcriptional repression of C/EBPα and peroxisome proliferator-activated receptor γ2 (PPARγ2). However, LCoR overexpression did not affect the recruitment of C/EBPβ to the promoters of C/EBPα and PPARγ2 in 3T3-L1 adipocytes. Of note, restoration of PPARγ2 or C/EBPα expression attenuated the inhibitory effect of LCoR on adipogenesis. Mechanistically, LCoR suppressed C/EBPβ-mediated transcription by recruiting C-terminal binding proteins to the C/EBPα and PPARγ2 promoters and by modulating histone modifications. Taken together, our results indicate that LCoR negatively regulates early adipogenesis by repressing C/EBPβ transcriptional activity and add LCoR to the growing list of transcriptional corepressors of adipogenesis.

Endothelial LRP1 regulates metabolic responses by acting as a co-activator of PPARγ

Low-density lipoprotein receptor-related protein 1 (LRP1) regulates lipid and glucose metabolism in liver and adipose tissue. It is also involved in central nervous system regulation of food intake and leptin signalling. Here we demonstrate that endothelial Lrp1 regulates systemic energy homeostasis. Mice with endothelial-specific Lrp1 deletion display improved glucose sensitivity and lipid profiles combined with increased oxygen consumption during high-fat-diet-induced obesity. We show that the intracellular domain of Lrp1 interacts with the nuclear receptor Pparγ, a central regulator of lipid and glucose metabolism, acting as its transcriptional co-activator in endothelial cells. Therefore, Lrp1 not only acts as an endocytic receptor but also directly participates in gene transcription. Our findings indicate an underappreciated functional role of endothelium in maintaining systemic energy homeostasis.

Nck2, an unexpected regulator of adipogenesis

The regulation of adipose tissue expansion by adipocyte hypertrophy and/or hyperplasia is the topic of extensive investigations given the potential differential contribution of the 2 processes to the development of numerous chronic diseases associated with obesity. We recently discovered that the loss-of-function of the Src homology domain-containing protein Nck2 in mice promotes adiposity accompanied with adipocyte hypertrophy and impaired function, and enhanced adipocyte differentiation in vitro. Moreover, in severely-obese human's adipose tissue, we found that Nck2 expression is markedly downregulated. In this commentary, our goal is to expand upon additional findings providing further evidence for a unique Nck2-dependent mechanism regulating adipogenesis. We propose that Nck2 should be further investigated as a regulator of the reliance of white adipose tissue on hyperplasia versus hypertrophy during adipose tissue expansion, and hence, as a potential novel molecular target in obesity.

C-terminus of HSC70-Interacting Protein (CHIP) Inhibits Adipocyte Differentiation via Ubiquitin- and Proteasome-Mediated Degradation of PPARγ

PPARγ (Peroxisome proliferator-activated receptor γ) is a nuclear receptor involved in lipid homeostasis and related metabolic diseases. Acting as a transcription factor, PPARγ is a master regulator for adipocyte differentiation. Here, we reveal that CHIP (C-terminus of HSC70-interacting protein) suppresses adipocyte differentiation by functioning as an E3 ligase of PPARγ. CHIP directly binds to and induces ubiquitylation of the PPARγ protein, leading to proteasome-dependent degradation. Stable overexpression or knockdown of CHIP inhibited or promoted adipogenesis, respectively, in 3T3-L1 cells. On the other hand, a CHIP mutant defective in E3 ligase could neither regulate PPARγ protein levels nor suppress adipogenesis, indicating the importance of CHIP-mediated ubiquitylation of PPARγ in adipocyte differentiation. Lastly, a CHIP null embryo fibroblast exhibited augmented adipocyte differentiation with increases in PPARγ and its target protein levels. In conclusion, CHIP acts as an E3 ligase of PPARγ, suppressing PPARγ-mediated adipogenesis.

Potential of Natural Products in the Inhibition of Adipogenesis through Regulation of PPARγ Expression and/or Its Transcriptional Activity

Obesity is a global health problem characterized as an increase in the mass of adipose tissue. Adipogenesis is one of the key pathways that increases the mass of adipose tissue, by which preadipocytes mature into adipocytes through cell differentiation. Peroxisome proliferator-activated receptor γ (PPARγ), the chief regulator of adipogenesis, has been acutely investigated as a molecular target for natural products in the development of anti-obesity treatments. In this review, the regulation of PPARγ expression by natural products through inhibition of CCAAT/enhancer-binding protein β (C/EBPβ) and the farnesoid X receptor (FXR), increased expression of GATA-2 and GATA-3 and activation of the Wnt/β-catenin pathway were analyzed. Furthermore, the regulation of PPARγ transcriptional activity associated with natural products through the antagonism of PPARγ and activation of Sirtuin 1 (Sirt1) and AMP-activated protein kinase (AMPK) were discussed. Lastly, regulation of mitogen-activated protein kinase (MAPK) by natural products, which might regulate both PPARγ expression and PPARγ transcriptional activity, was summarized. Understanding the role natural products play, as well as the mechanisms behind their regulation of PPARγ activity is critical for future research into their therapeutic potential for fighting obesity.