Nuclear Peroxisome Proliferator-activated Receptor Research Articles

The loss of the hormonal function of bilirubin induces adiposity in male and female mice

The prevalence of obesity and its related comorbidities, including diabetes and metabolic dysfunction associated fatty liver disease (MAFLD), are on the rise globally, indicating the importance of new therapeutics for these diseases. Interestingly, serum bilirubin levels are negatively correlated with obesity, diabetes, and MAFLD. We have previously generated pegylated bilirubin nanoparticles (PEGBR) and demonstrated their therapeutic potential in the treatment of obesity and MAFLD. However, it’s unknown whether their beneficial effects are due to bilirubin’s antioxidant properties or its hormonal function by binding to and activating the nuclear receptor peroxisome proliferator-activated receptor alpha (PPARa). To determine this, we used female and male hepatocyte-specific PPARa knockout mice ( PparaHepKO) and floxed ( Pparaflox) control mice on a high-fat diet for 30 weeks to induce adiposity and MAFLD. The mice were treated with vehicle or PEGBR (30 mg/kg) for six weeks. In female Pparaflox mice, PEGBR significantly lowered body weight, but not in the female PparaHepKO mice. A similar trend was seen in the male Pparaflox mice but was not statistically significant. PEGBR significantly reduced hepatic fat mass and triglycerides in the female and male Pparaflox mice but not in the PparaHepKO mice. Using lipidomics, we determined the lipid composition of the liver and how PEGBR changed it. In the male Pparaflox mice, PEGBR significantly reduced 109 lipid species, whereas, in the male PparaHepKO mice, PEGBR only reduced 7 species (93.6% reduction). In the female PparaHepKO mice, there was a 2.7% reduction in the number of lipid species significantly decreased by PEGBR compared to Pparaflox controls. Male Pparaflox mice had an increase in plasma high-density lipoprotein cholesterol and a decrease in very-low-density particle number with PEGBR, but this was not seen in the male PparaHepKO or female mice. In addition to protecting against the development of MAFLD, PEGBR significantly reduced fasting blood glucose and insulin levels only in the Pparaflox mice. Overall, the data indicates that the protective effects of bilirubin on obesity, MAFLD, and glucose tolerance are due to its hormonal function through PPARa. This study also confirms the therapeutic potential of bilirubin nanoparticles for obesity and its associated comorbidities. This work was supported by the National Institutes of Health F31HL170972 (Z.A.K.) and R01DK121797 (T.D.H.J.) and R01DA058933 (T.D.H.J.). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Sulfonylureas exert antidiabetic action on adipocytes by inhibition of PPARγ serine 273 phosphorylation

ObjectiveSulfonylureas (SUs) are still among the mostly prescribed antidiabetic drugs with an established mode of action: release of insulin from pancreatic β-cells. In addition, effects of SUs on adipocytes by activation of the nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) have been described, which might explain their insulin-sensitizing potential observed in patients. However, there is a discrepancy between the impact of SUs on antidiabetic action and their rather moderate in vitro effect on PPARγ transcriptional activity. Recent studies have shown that some PPARγ ligands can improve insulin sensitivity by blocking PPARγ Ser-273 phosphorylation without having full agonist activity. It is unknown if SUs elicit their antidiabetic effects on adipocytes by inhibition of PPARγ phosphorylation. Here, we investigated if binding of SUs to PPARγ can interfere with PPARγ Ser-273 phosphorylation and determined their antidiabetic actions in vitro in primary human white adipocytes and in vivo in high-fat diet (HFD) obese mice. MethodsPrimary human white preadipocytes were differentiated in the presence of glibenclamide, glimepiride and PPARγ ligands rosiglitazone and SR1664 to compare PPARγ Ser-273 phosphorylation, glucose uptake and adipokine expression. Transcriptional activity at PPARγ was determined by luciferase assays, quantification of PPARγ Ser-273 phosphorylation was determined by Western blotting and CDK5 kinase assays. In silico modelling was performed to gain insight into the binding characteristics of SUs to PPARγ. HFD mice were administered SUs and rosiglitazone for 6 days. PPARγ Ser-273 phosphorylation in white adipose tissue (WAT), body composition, glucose tolerance, adipocyte morphology and expression levels of genes involved in PPARγ activity in WAT and brown adipose tissue (BAT) were evaluated. ResultsSUs inhibit phosphorylation of PPARγ at Ser-273 in primary human white adipocytes and exhibit a positive antidiabetic expression profile, which is characterized by up regulation of insulin-sensitizing and down regulation of insulin resistance-inducing adipokines. We demonstrate that SUs directly bind to PPARγ by in silico modelling and inhibit phosphorylation in kinase assays to a similar extend as rosiglitazone and SR1664. In HFD mice SUs reduce PPARγ phosphorylation in WAT and have comparable effects on gene expression to rosiglitazone. In BAT SUs increase UCP1 expression and reduce lipid droplets sizes. ConclusionsOur findings indicate that a part of SUs extra-pancreatic effects on adipocytes in vitro and in vivo is probably mediated via their interference with PPARγ phosphorylation rather than via classical agonistic activity at clinical concentrations.

Regulatory Effect of Osteocytes on Extramedullary and Bone Marrow Adipose Tissue Development and Function.

This review summarizes evidence on osteocyte support of extramedullary and bone marrow adipocyte development and discusses the role of endogenous osteocyte activities of nuclear receptors peroxisome proliferator-activated receptor gamma (PPARG) and alpha (PPARA) in this support. PPARG and PPARA proteins, key regulators of glucose and fatty acid metabolism, are highly expressed in osteocytes. They play significant roles in the regulation of osteocyte secretome and osteocyte bioenergetics; both activities contributing to the levels of systemic energy metabolism in part through an effect on metabolic function of extramedullary and bone marrow adipocytes. The PPARs-controlled osteocyte endocrine/paracrine activities, including sclerostin expression, directly regulate adipocyte function, while the PPARs-controlled osteocyte fuel utilization and oxidative phosphorylation contribute to the skeletal demands for glucose and fatty acids, whose availability is under the control of adipocytes. Bone is an inherent element of systemic energy metabolism with PPAR nuclear receptors regulating osteocyte-adipocyte metabolic axes.

Design, synthesis, and biological evaluation of piperazine derivatives as pan-PPARs agonists for the treatment of liver fibrosis

Liver fibrosis is commonly occurred in chronic liver diseases, but there is no approved drug for clinical use. The nuclear receptor peroxisome proliferator-activated receptors (PPARs) could not only regulate metabolic homeostasis but also possess anti-inflammatory and antifibrotic effects, and pan-PPARs agonist was considered as a potential anti-liver fibrosis agent. In this study, a series of novel piperazine pan-PPARs agonists were developed, and the preferred compound 12 displayed potent and well-balanced pan-PPARs agonistic activity. Moreover, compound 12 could dose-dependently stimulate the PPARs target genes expression and showed high selectivity over other related nuclear receptors. Importantly, compound 12 exhibited excellent pharmacokinetic profiles and good anti-liver fibrosis effects in vivo. Collectively, compound 12 holds promise for developing an anti-liver fibrosis agent.

A structural basis for the activation of peroxisome proliferator-activated receptor gamma (PPARγ) by perfluorooctanoic acid (PFOA)

Perfluorooctanoic acid (PFOA) is a widespread environmental pollutant of the perfluoroalkyl substance (PFAS) class that is extremely resistant to environmental and metabolic degradation, leading to bioaccumulation. PFOA exposure has been linked to many health effects including endocrine disruption and metabolic dysregulation, but our understanding of the molecular mechanisms resulting in these outcomes remains incomplete. One target affected by PFOA is the ligand regulated nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) which plays a critical role in controlling metabolic homeostasis through regulating processes such as adipogenesis, glucose homeostasis, inflammation and osteogenesis. It has been previously established that PFOA activates PPARγ through binding to the PPARγ ligand binding domain (PPARγ LBD) leading to increased expression of PPARγ controlled target genes. However, the mechanism by which PFOA achieves this has remained elusive. Here, we employed a combination of X-ray crystallography and fluorescence polarization assays to provide a structural basis for PFOA mediated activation of PPARγ via binding to the PPARγ LBD. Using X-ray crystallography, the cocrystal structure of the PPARγ LBD:PFOA complex was solved. This revealed that PFOA occupies three distinct sites, two within the PPARγ LBD and one within the activation function 2 (AF2) on the protein surface. Structural comparison of PFOA binding with previously reported PPARγ:ligand complexes supports that PFOA activates PPARγ by a partial agonist mechanism at micromolar concentrations. Fluorescence polarization assays also revealed that PFOA binding to the AF2 is unlikely to occur in a cellular context and confirmed that PFOA behaves as a partial agonist in vitro, weakly recruiting a coactivator peptide to the AF2 of the PPARγ LBD. This discovery provides an advancement in understanding PFOA mediated regulation of PPARγ, giving new insight regarding regulation of PPARγ by PFAS and PFAS substitutes in general and can be applied to the design and assessment of safer PFAS.

Serum adiponectin and peroxisome proliferator-activated receptors-γ levels in obese patients with and without prediabetes.

Obesity is an increasingly prevalent global health problem, which is generally caused by the increase in body fat mass above normal and observed in all societies. If the blood glucose level is higher than normal but not high enough to diagnose diabetes, this condition is defined as prediabetes. Adiponectin increases fatty acid oxidation and insulin sensitivity and is closely associated with obesity. One of the nuclear receptor superfamily member peroxisome proliferator-activated receptors is shown to have an important role in various metabolic reactions. This study aimed to investigate the serum levels of adiponectin and peroxisome proliferator-activated receptors-gamma parameters, which are closely related to adipose tissue, energy metabolism, and insulin sensitivity, in obese patients with and without prediabetes. For this purpose, 52 obese patients with prediabetes, 48 obese patients with non-prediabetes, and 76 healthy individuals were included in this study. Serum adiponectin and peroxisome proliferator-activated receptors-γ levels were analyzed by ELISA. Serum adiponectin levels were significantly higher in obese patients with prediabetes (18.15±15.99) compared with the control group (15.17±15.67; p=0.42). No significant difference was observed in both adiponectin and peroxisome proliferator-activated receptors-γ levels in the obese patients with the non-prediabetes group compared with the control group. However, no significant difference was observed in the obese patients with prediabetes group and obese patients with non-prediabetes group. Our results suggest that adiponectin may serve as an indicator of prediabetes. This implies that examining adiponectin levels in individuals diagnosed with prediabetes may enhance our understanding of the metabolic processes closely linked to prediabetes and related conditions.

Orthogonal assay and QSAR modelling of Tox21 PPARγ antagonist in vitro high-throughput screening assay

Disruption of signalling mediated by the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) is associated with risk of cancer, metabolic diseases, and endocrine disruption. The purpose of this study was to identify environmental chemicals acting as PPARγ antagonists. Data from the Tox21 PPARγ antagonism assay were replicated using a reporter system in HEK293 cells. Two quantitative structure-activity relationship (QSAR) models were developed, and five REACH-registered substances predicted positive were tested in vitro. Reporter assay results were consistent with Tox21 data since all conflicting results could be explained by assay interference. QSAR models showed good predictive performance, and follow-up experiments revealed two PPARγ antagonists out of three non-interfering chemicals. In conclusion, the developed QSAR models and follow-up experiments are important steps in the discovery of potential endocrine- and metabolism-disrupting chemicals.

The nuclear cytokine IL-37a controls lethal cytokine storms primarily via IL-1R8-independent transcriptional upregulation of PPARγ.

Cytokine storms are crucial in the development of various inflammatory diseases, including sepsis and autoimmune disorders. The immunosuppressive cytokine INTERLEUKIN (IL)-37 consists of five isoforms (IL-37a-e). We identified IL-37a as a nuclear cytokine for the first time. Compared to IL-37b, IL-37a demonstrated greater efficacy in protecting against Toll-like receptor-induced cytokine hypersecretion and lethal endotoxic shock. The full-length (FL) form of IL-37a and the N-terminal fragment, which is processed by elastase, could translocate into cell nuclei through a distinctive nuclear localization sequence (NLS)/importin nuclear transport pathway. These forms exerted their regulatory effects independent of the IL-1R8 receptor by transcriptionally upregulating the nuclear receptor peroxisome proliferator-activated receptor (PPARγ). This process involved the recruitment of the H3K4 methyltransferase complex WDR5/MLL4/C/EBPβ and H3K4me1/2 to the enhancer/promoter of Pparg. The receptor-independent regulatory pathway of the nuclear IL-37a-PPARγ axis and receptor-dependent signaling by secreted IL-37a maintain homeostasis and are potential therapeutic targets for various inflammatory diseases, including sepsis.

Andrographolide attenuated MCT-induced HSOS via regulating NRF2-initiated mitochondrial biogenesis and antioxidant response.

Hepatic sinusoidal obstruction syndrome (HSOS) is a death-dealing liver disease with a fatality rate of up to 67%. In the study present, we explored the efficacy of andrographolide (Andro), a diterpene lactone from Andrographis Herba, in ameliorating the monocrotaline (MCT)-induced HSOS and the underlying mechanism. The alleviation of Andro on MCT-induced rats HSOS was proved by biochemical index detection, electron microscope observation, and liver histological evaluation. Detection of hepatic ATP content, mitochondrial DNA (mtDNA) copy number, and protein expression of nuclear respiratory factor-1 (NRF1) and peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PPARGC1A) demonstrated that Andro strengthened mitochondrial biogenesis in livers from MCT-treated rats. Chromatin immunoprecipitation assay exhibited that Andro enhanced the occupation of nuclear factor erythroid 2-related factor 2 (NFE2L2, also known as NRF2) in the promoter regions of both PPARGC1A and NRF1. Andro also activated the NRF2-dependent anti-oxidative response and alleviated liver oxidative injury. In Nrf2 knock-out mice, MCT induced more severe liver damage, and Andro showed no alleviation in it. Furthermore, the Andro-activated mitochondrial biogenesis and anti-oxidative response were reduced in Nrf2 knock-out mice. Contrastingly, knocking out Kelch-like ECH-associated protein 1 (Keap1), a NRF2 repressor, reduced MCT-induced liver damage. Results from co-immunoprecipitation, molecular docking analysis, biotin-Andro pull-down, cellular thermal shift assay, and surface plasmon resonance assay showed that Andro hindered the NRF2-KEAP1 interaction via directly binding to KEAP1. In conclusion, our results revealed that NRF2-dependent liver mitochondrial biogenesis and anti-oxidative response were essential for the Andro-provided alleviation of the MCT-induced HSOS. Graphical Headlights: 1. Andro alleviated MCT-induced HSOS via activating antioxidative response and promoting mitochondrial biogenesis. 2. Andro-activated antioxidative response and mitochondrial biogenesis were NRF2-dependent. 3. Andro activated NRF2 via binding to KEAP1.

Identification of phytochemicals as putative ligands for the targeted modulation of peroxisome proliferator‐activated receptor α (PPARα) in animals

The PPAR family of transcription factors are ligand-activated and regulate diverse functions including metabolic, neurological, and inflammatory diseases, neurodegenerative disorders, fertility or reproduction in the body. Specifically, PPARα is known to play a role in reducing the levels of circulating triglycerides and regulating energy homeostasis in livestock animals. This study aimed to identify phytochemicals that could serve as ligands for modulation of the bovine nuclear peroxisome proliferator-activated receptor alpha (PPARα) using molecular docking studies. Therefore, we investigated 1000 flavonoids belonging to different groups for their ability to bind to PPARα using molecular docking. Out of 1000, 6 top lead compounds with maximum binding affinity, evaluated through molecular docking, were further analysed for physicochemical properties and drug-likeness attributes. The results revealed that two flavonoids, Quercetin-3-o-rhamnoside and (-)- epicatechingallate, which are known fatty acid synthase inhibitors, demonstrated high docking scores with PPARα (−8.66 kcal/mol and −8.49 kcal/mol, respectively) and low RMSD values with PPARα (1.61 kcal/mol and 1.28 kcal/mol, respectively) as compared to PPARα agonist (synthetic), fenofibrate (−6.24 kcal/mol and 2.19 kcal/mol) and thus analyzed further for prediction of stability of docked complexes through MD simulations. MD simulation studies predicted the stability of complexes and the complex of Quercetin-3-o-rhamnoside and (-)- epicatechingallate were found to be stable at 100 ns based on RSMD value and RMSF residue index. Through computational analysis, the screened compounds showed good pharmacokinetic parameters, including non-toxicity, non-carcinogenic, high gastrointestinal absorption and thus can serve as potential drug candidates. Finally, the findings suggest that these phytochemicals have the potential to act as potent PPARα pharmacological agonists to prevent disease mechanisms and their related complications, providing insights into the role of phytochemicals as feed additives in animals for modulating PPARα functions. Communicated by Ramaswamy H. Sarma

Natural Product Ligands of the Peroxisome Proliferator-Activated Receptor Gamma as Anti-Inflammatory Mediators

Abstract: Immunologists have long considered inflammation to be a two-edged sword. Short-term inflammation can be beneficial, but long-term chronic inflammation is damaging. Obesity, type 2 diabetes (T2D), and cancer have recently been added to the never-ending list of inflammatory diseases. The nuclear transcription factor peroxisome proliferator-activated receptor gamma (PPAR-γ) is involved in inflammation and obesity. Clinicians employed PPAR-γ agonists, both synthetic and natural, to treat disorders such as obesity and T2D without fully understanding the biochemical features and potential adverse effects. This is one of the reasons for the controversy surrounding the thiazolidinedione class of medicines, including rosiglitazone and pioglitazone. Nonetheless, various natural PPAR-γ ligands, including endogenous physiological ligands, are discovered regularly around the world. This review aims to summarise the physiochemical properties and possible antiinflammatory actions of ligands discovered in nature. Future research in this area should be supported in order to find improved commercial PPAR-γ ligand anti-inflammatory products.

Nuclear hormone receptor NHR-49 is an essential regulator of stress resilience and healthy aging in Caenorhabditis elegans.

The genome of Caenorhabditis elegans encodes 284 nuclear hormone receptor, which perform diverse functions in development and physiology. One of the best characterized of these is NHR-49, related in sequence and function to mammalian hepatocyte nuclear factor 4α and peroxisome proliferator-activated receptor α. Initially identified as regulator of lipid metabolism, including fatty acid catabolism and desaturation, additional important roles for NHR-49 have since emerged. It is an essential contributor to longevity in several genetic and environmental contexts, and also plays vital roles in the resistance to several stresses and innate immune response to infection with various bacterial pathogens. Here, we review how NHR-49 is integrated into pertinent signaling circuits and how it achieves its diverse functions. We also highlight areas for future investigation including identification of regulatory inputs that drive NHR-49 activity and identification of tissue-specific gene regulatory outputs. We anticipate that future work on this protein will provide information that could be useful for developing strategies to age-associated declines in health and age-related human diseases.

Disclosing Environmental Ligands of L-FABP and PPARγ: Should We Re-evaluate the Chemical Safety of Hydrocarbon Surfactants?

Chemical contaminants can cause adverse effects by binding to the liver-fatty acid binding protein (L-FABP) and peroxisome proliferator-activated nuclear receptor γ (PPARγ), which are vital in lipid metabolism. However, the presence of numerous compounds in the environment has hindered the identification of their ligands, and thus only a small portion have been discovered to date. In this study, protein Affinity Purification with Nontargeted Analysis (APNA) was employed to identify the ligands of L-FABP and PPARγ in indoor dust and sewage sludge. A total of 83 nonredundant features were pulled-out by His-tagged L-FABP as putative ligands, among which 13 were assigned as fatty acids and hydrocarbon surfactants. In contrast, only six features were isolated when His-tagged PPARγ LBD was used as the protein bait. The binding of hydrocarbon surfactants to L-FABP and PPARγ was confirmed using both recombinant proteins and reporter cells. These hydrocarbon surfactants, along with >50 homologues and isomers, were detected in dust and sludge at high concentrations. Fatty acids and hydrocarbon surfactants explained the majority of L-FABP (57.7 ± 32.9%) and PPARγ (66.0 ± 27.1%) activities in the sludge. This study revealed hydrocarbon surfactants as the predominant synthetic ligands of L-FABP and PPARγ, highlighting the importance of re-evaluating their chemical safety.

Antidiabetic agents as a novel treatment for Alzheimer's and Parkinson's disease.

Therapeutic strategies for neurodegenerative disorders have commonly targeted individual aspects of the disease pathogenesis to little success. Neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD), are characterized by several pathological features. In AD and PD, there is an abnormal accumulation of toxic proteins, increased inflammation, decreased synaptic function, neuronal loss, increased astrocyte activation, and perhaps a state of insulin resistance. Epidemiological evidence has revealed a link between AD/PD and type 2 diabetes mellitus, with these disorders sharing some pathological commonalities. Such a link has opened up a promising avenue for repurposing antidiabetic agents in the treatment of neurodegenerative disorders. A successful therapeutic strategy for AD/PD would likely require a single or several agents which target the separate pathological processes in the disease. Targeting cerebral insulin signalling produces numerous neuroprotective effects in preclinical AD/PD brain models. Clinical trials have shown the promise of approved diabetic compounds in improving motor symptoms of PD and preventing neurodegenerative decline, with numerous further phase II trials and phase III trials underway in AD and PD populations. Alongside insulin signalling, targeting incretin receptors in the brain represents one of the most promising strategies for repurposing currently available agents for the treatment of AD/PD. Most notably, glucagon-like-peptide-1 (GLP-1) receptor agonists have displayed impressive clinical potential in preclinical and early clinical studies. In AD the GLP-1 receptor agonist, liraglutide, has been demonstrated to improve cerebral glucose metabolism and functional connectivity in small-scale pilot trials. Whilst in PD, the GLP-1 receptor agonist exenatide is effective in restoring motor function and cognition. Targeting brain incretin receptors reduces inflammation, inhibits apoptosis, prevents toxic protein aggregation, enhances long-term potentiation and autophagy as well as restores dysfunctional insulin signalling. Support is also increasing for the use of additional approved diabetic treatments, including intranasal insulin, metformin hydrochloride, peroxisome proliferator-activated nuclear receptor γ agonists, amylin analogs, and protein tyrosine phosphatase 1B inhibitors which are in the investigation for deployment in PD and AD treatment. As such, we provide a comprehensive review of several promising anti-diabetic agents for the treatment of AD and PD.

Medium-chain fatty acids modify macrophage expression of metabolic and inflammatory genes in a PPAR β/δ-dependent manner

There is great interest on medium chain fatty acids (MCFA) for cardiovascular health. We explored the effects of MCFA on the expression of lipid metabolism and inflammatory genes in macrophages, and the extent to which they were mediated by the nuclear receptor peroxisome proliferator-activated receptor beta/delta (PPAR β/δ). J774A.1 murine macrophages were exposed to octanoate or decanoate as MCFA, a long-chain fatty acid control (palmitate), or the PPAR β/δ agonist GW501516, with or without lipopolysaccharide (LPS) stimulation, and with or without an siRNA-induced knockdown of PPAR β/δ. MCFA increased the expression of Plin2, encoding a lipid-droplet associated protein with anti-inflammatory effects in macrophages, in a partially PPAR β/δ-dependent manner. Both MCFA stimulated expression of the cholesterol efflux pump ABCA1, more pronouncedly under LPS stimulation and in the absence of PPAR β/δ. Octanoate stimulated the expression of Pltp, encoding a phospholipid transfer protein that aids ABCA1 in cellular lipid efflux. Only palmitate increased expression of the proinflammatory genes Il6, Tnf, Nos2 and Mmp9. Non-stimulated macrophages exposed to MCFA showed less internalization of fluorescently labeled lipoproteins. MCFA influenced the transcriptional responses of macrophages favoring cholesterol efflux and a less inflammatory response compared to palmitate. These effects were partially mediated by PPAR β/δ.

Brown Adipose Tissue PPARγ Is Required for the Insulin-Sensitizing Action of Thiazolidinediones.

Brown adipose tissue (BAT) plays a critical role in metabolic homeostasis. BAT dysfunction is associated with the development of obesity through an imbalance between energy expenditure and energy intake. The nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) is the master regulator of adipogenesis. However, the roles of PPARγ and thiazolidinediones (TZDs) in the regulation of BAT metabolism remain unclear. TZDs, which are selective PPARγ activators, improve systemic insulin resistance in animals and humans. In the present study, we generated brown adipocyte-specific PPARγ-deficient mice (BATγKO) to examine the in vivo roles of PPARγ and TZDs in BAT metabolism. In electron microscopic examinations, brown adipocyte-specific PPARγ deletion promoted severe whitening of brown fat and morphological alteration of mitochondria. Brown adipocyte-specific PPARγ deletion also reduced mRNA expression of BATselective genes. Although there was no difference in energy expenditure between control and BATγKO mice in calorimetry, norepinephrine-induced thermogenesis was impaired in BATγKO mice. Moreover, pioglitazone treatment improved diet-induced insulin resistance in the control mice but not in the BATγKO mice. These findings suggest that BAT PPARγ is necessary for the maintenance of brown adipocyte function and for the insulin-sensitizing action of TZDs.

Transcriptional regulation of adipogenin expression in liver steatosis by hepatic peroxisome proliferator-activated receptor gamma.

The nuclear receptors peroxisome proliferator-activated receptor gamma (PPARγ) and adipogenin (ADIG) play vital roles in lipid metabolism. However, the interaction between PPARγ and ADIG during liver steatosis remains unclear. In this study, we aimed to investigate the role of PPARγ in the transcriptional regulation of hepatic ADIG expression. Adig was found to be highly expressed in various fatty liver mouse models. Although hepatic Adig was expressed at high levels in the fatty liver of type 2 diabetic ob/ob mice and was upregulated by PPARγ agonist treatment, it was expressed at significantly low levels in liver-specific Pparg-knockout mice. Moreover, hepatic Adig expression was observed in other mouse models of liver steatosis, such as the leptin receptor mutant db/db and alcohol-fed mice. Adig was also highly expressed in the white and brown adipose tissues, skeletal muscles, and heart of ob/ob mice. Reporter and electromobility shift assays showed that PPARγ positively regulates Adig transcriptional activity by directly binding to a functional PPARγ-responsive element in the promoter region. Our results indicate that Adig is a novel target gene of hepatic PPARγ in liver steatosis.

GDE7 produces cyclic phosphatidic acid in the ER lumen functioning as a lysophospholipid mediator

Cyclic phosphatidic acid (cPA) is a lipid mediator, which regulates adipogenic differentiation and glucose homeostasis by suppressing nuclear peroxisome proliferator-activated receptor γ (PPARγ). Glycerophosphodiesterase 7 (GDE7) is a Ca2+-dependent lysophospholipase D that localizes in the endoplasmic reticulum. Although mouse GDE7 catalyzes cPA production in a cell-free system, it is unknown whether GDE7 generates cPA in living cells. Here, we demonstrate that human GDE7 possesses cPA-producing activity in living cells as well as in a cell-free system. Furthermore, the active site of human GDE7 is directed towards the luminal side of the endoplasmic reticulum. Mutagenesis revealed that amino acid residues F227 and Y238 are important for catalytic activity. GDE7 suppresses the PPARγ pathway in human mammary MCF-7 and mouse preadipocyte 3T3-L1 cells, suggesting that cPA functions as an intracellular lipid mediator. These findings lead to a better understanding of the biological role of GDE7 and its product, cPA.

Fatty acid desaturation by stearoyl-CoA desaturase-1 controls regulatory T cell differentiation and autoimmunity

The imbalance between pathogenic and protective T cell subsets is a cardinal feature of autoimmune disorders such as multiple sclerosis (MS). Emerging evidence indicates that endogenous and dietary-induced changes in fatty acid metabolism have a major impact on both T cell fate and autoimmunity. To date, however, the molecular mechanisms that underlie the impact of fatty acid metabolism on T cell physiology and autoimmunity remain poorly understood. Here, we report that stearoyl-CoA desaturase-1 (SCD1), an enzyme essential for the desaturation of fatty acids and highly regulated by dietary factors, acts as an endogenous brake on regulatory T-cell (Treg) differentiation and augments autoimmunity in an animal model of MS in a T cell-dependent manner. Guided by RNA sequencing and lipidomics analysis, we found that the absence of Scd1 in T cells promotes the hydrolysis of triglycerides and phosphatidylcholine through adipose triglyceride lipase (ATGL). ATGL-dependent release of docosahexaenoic acid enhanced Treg differentiation by activating the nuclear receptor peroxisome proliferator-activated receptor gamma. Our findings identify fatty acid desaturation by SCD1 as an essential determinant of Treg differentiation and autoimmunity, with potentially broad implications for the development of novel therapeutic strategies and dietary interventions for autoimmune disorders such as MS.

Concomitant inhibition of PPARγ and mTORC1 induces the differentiation of human monocytes into highly immunogenic dendritic cells

Monocytes can differentiate into macrophages (Mo-Macs) or dendritic cells (Mo-DCs). The cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) induces the differentiation of monocytes into Mo-Macs, while the combination of GM-CSF/interleukin (IL)-4 is widely used to generate Mo-DCs for clinical applications and to study human DC biology. Here, we report that pharmacological inhibition of the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) in the presence of GM-CSF and the absence of IL-4 induces monocyte differentiation into Mo-DCs. Remarkably, we find that simultaneous inhibition of PPARγ and the nutrient sensor mammalian target of rapamycin complex 1 (mTORC1) induces the differentiation of Mo-DCs with stronger phenotypic stability, superior immunogenicity, and a transcriptional profile characterized by a strong type I interferon (IFN) signature, a lower expression of a large set of tolerogenic genes, and the differential expression of several transcription factors compared with GM-CSF/IL-4 Mo-DCs. Our findings uncover a pathway that tailors Mo-DC differentiation with potential implications in the fields of DC vaccination and cancer immunotherapy.