Coactivators in PPAR-Regulated Gene Expression. PPAR Res. 2010;2010. [PMID: 20814439 PMCID: PMC2929611 DOI: 10.1155/2010/250126]

PPARs in liver physiology

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors and transcriptional modulators with crucial functions in hepatic and whole-body energy homeostasis. Besides their well-documented roles in lipid and glucose metabolism, emerging evidence also implicate PPARs in the control of other processes such as inflammatory responses. Recent technological advances, such as single-cell RNA sequencing, have allowed to unravel an unexpected complexity in the regulation of PPAR expression, activity and downstream signaling. Here we provide an overview of the latest advances in the study of PPARs in liver physiology, with a specific focus on formerly neglected aspects of PPAR regulation, such as tissular zonation, cellular heterogeneity, circadian rhythms, sexual dimorphism and species-specific features.

Maternal vitamin D deficiency influences long-chain polyunsaturated fatty acids and pregnancy outcome in association with alterations in one-carbon metabolism

Preeclampsia is a pregnancy-specific disorder, leading to maternal and infant morbidity and mortality. Abnormal placentation has been reported in preeclampsia. Nutrients like vitamin D and long-chain polyunsaturated fatty acids (LCPUFA) are known to play a role in placental development. In an animal model, we have previously demonstrated that maternal vitamin D deficiency increases the thromboxane/prostacyclin ratio and contributes to inflammation and vasoconstriction. We hypothesize that maternal vitamin D status influences placental LCPUFA metabolism through alterations in one carbon metabolism in women with preeclampsia. To test this hypothesis, we recruited 69 normotensive control (NC) women and 50 women with preeclampsia. Women with preeclampsia had lower placental protein and mRNA levels of cystathionine-β-synthase (CBS), higher plasma malondialdehyde (MDA) levels and higher levels of arachidonic acid (AA) and total omega-6 fatty acids in the placenta. Women with preeclampsia also demonstrated higher placental mRNA levels of cyclooxygenase-2 (COX-2) as compared to NC women. Maternal 25(OH)D levels were negatively associated with maternal plasma MDA levels. Placental vitamin D receptor (VDR) levels were positively associated with CBS while maternal MDA levels were positively associated with serum levels of thromboxane-B2 (TXB2) levels. Our findings indicate that vitamin D deficiency increases oxidative stress through alterations in one carbon metabolism to influence pro-inflammatory omega-6 metabolic pathway in the placenta. This study demonstrates a possible mechanism through which vitamin D deficiency can result in an imbalance in the LCPUFA metabolites and contribute to placental inflammation and endothelial dysfunction in preeclampsia.

Reduced peroxisomal import triggers peroxisomal retrograde signaling

Maintaining organelle function in the face of stress is known to involve organelle-specific retrograde signaling. Using Caenorhabditis elegans, we present evidence of the existence of such retrograde signaling for peroxisomes, which we define as the peroxisomal retrograde signaling (PRS). Specifically, we show that peroxisomal import stress caused by knockdown of the peroxisomal matrix import receptor prx-5/PEX5 triggers NHR-49/peroxisome proliferator activated receptor alpha (PPARα)- and MDT-15/MED15-dependent upregulation of the peroxisomal Lon protease lonp-2/LONP2 and the peroxisomal catalase ctl-2/CAT. Using proteomic and transcriptomic analyses, we show that proteins involved in peroxisomal lipid metabolism and immunity are also upregulated upon prx-5(RNAi). While the PRS can be triggered by perturbation of peroxisomal β-oxidation, we also observed hallmarks of PRS activation upon infection with Pseudomonas aeruginosa. We propose that the PRS, in addition to a role in lipid metabolism homeostasis, may act as a surveillance mechanism to protect against pathogens.

L-carnitine exerts a nutrigenomic effect via direct modulation of nuclear receptor signaling in adipocytes, hepatocytes and SKMC, demonstrating its nutritional impact

L-carnitine is an indispensable metabolite facilitating the transport of fatty acids into the mitochondrial matrix and has been previously postulated to exert a nutrigenomic effect. However, the underlying molecular mechanisms remain mostly unclear. We hypothesized that L-carnitine interacts with nuclear receptors involved in metabolic regulation, thereby modulating downstream targets of cellular metabolism. Therefore, we investigated the effect of L-carnitine supplementation on protein activity, mRNA expression, and binding affinities of nuclear receptors as well as mRNA expression of downstream targets in skeletal muscle cells, hepatocytes, and differentiated adipocytes. L-carnitine supplementation to hepatocytes increased the protein activity of multiple nuclear receptors (RAR, RXR, VDR, PPAR, HNF4, ER, LXR). Diverging effects on the mRNA expression of PPAR-α, PPAR-δ, PPAR-γ, RAR-β, LXR-α, and RXR-α were observed in adipocytes, hepatocytes, and skeletal muscle cells. mRNA levels of PPAR-α, a key regulator of lipolysis and β-oxidation, were significantly upregulated, emphasizing a role of L-carnitine as a promoter of lipid catabolism. L-carnitine administration to hepatocytes modulated the transcription of key nuclear receptor target genes, including ALDH1A1, a promoter of adipogenesis, and OGT, a contributor to insulin resistance. Electrophoretic mobility shift assays proved L-carnitine to increase binding affinities of nuclear receptors to their promoter target sequences, suggesting a molecular mechanism for the observed transcriptional modulation. Overall, these findings indicate that L-carnitine modulates the activity and expression of nuclear receptors, thereby promoting lipolytic gene expression and decreasing transcription of target genes linked to adipogenesis and insulin resistance.

PPARα Between Aspirin and Plaque Clearance

Mounting evidence has identified that impaired amyloid-β (Aβ) clearance might contribute to Alzheimer's disease (AD) pathology. The lysosome-autophagy network plays an important role in protein homeostasis and cell health by removing abnormal protein aggregates via intracellular degradation. Therefore, stimulation of cellular degradative machinery for efficient removal of Aβ has emerged as a growing field in AD research. However, mechanisms controlling such pathways and drugs to promote such mechanisms are poorly understood. Aspirin is a widely used drug throughout the world and recent studies have identified a new function of this drug. At low doses, aspirin stimulates lysosomal biogenesis and autophagy to clear amyloid plaques in an animal model of AD. This review delineates such functions of aspirin and analyzes underlying mechanisms that involve peroxisome proliferator-activated receptor alpha (PPARα)-mediated transcription of transcription factor EB (TFEB), the master regulator of lysosomal biogenesis.

Protective Effects of (E)-β-Caryophyllene (BCP) in Chronic Inflammation

(E)-β-caryophyllene (BCP) is a bicyclic sesquiterpene widely distributed in the plant kingdom, where it contributes a unique aroma to essential oils and has a pivotal role in the survival and evolution of higher plants. Recent studies provided evidence for protective roles of BCP in animal cells, highlighting its possible use as a novel therapeutic tool. Experimental results show the ability of BCP to reduce pro-inflammatory mediators such as tumor necrosis factor-alfa (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), thus ameliorating chronic pathologies characterized by inflammation and oxidative stress, in particular metabolic and neurological diseases. Through the binding to CB2 cannabinoid receptors and the interaction with members of the family of peroxisome proliferator-activated receptors (PPARs), BCP shows beneficial effects on obesity, non-alcoholic fatty liver disease/nonalcoholic steatohepatitis (NAFLD/NASH) liver diseases, diabetes, cardiovascular diseases, pain and other nervous system disorders. This review describes the current knowledge on the biosynthesis and natural sources of BCP, and reviews its role and mechanisms of action in different inflammation-related metabolic and neurologic disorders.

A novel plausible mechanism of NSAIDs-induced apoptosis in cancer cells: the implication of proline oxidase and peroxisome proliferator-activated receptor

Although pharmaco-epidemiological studies provided evidence for the anticancer potential of non-steroidal anti-inflammatory drugs (NSAIDs), the mechanism of their anti-cancer activity is not known. Several lines of evidence suggest that proline dehydrogenase/proline oxidase (PRODH/POX) may represent a target for NSAIDs-dependent anti-cancer activity. PRODH/POX catalyzes conversion of proline into Δ1-pyrroline-5-carboxylate releasing ATP or reactive oxygen species for autophagy/apoptosis. Since NSAIDs are ligands of peroxisome proliferator-activated receptor (PPARs) and PPARs are implicated in PRODH/POX-dependent apoptosis we provided a hypothesis on the mechanism of NSAIDs-induced apoptosis in cancer cells.

Nuclear receptors in podocyte biology and glomerular disease

Nuclear receptors have a broad spectrum of biological functions in normal physiology and in the pathology of various diseases, including glomerular disease. The primary therapies for many glomerular diseases are glucocorticoids, which exert their immunosuppressive and direct podocyte protective effects via the glucocorticoid receptor (GR). As glucocorticoids are associated with important adverse effects and a substantial proportion of patients show resistance to these therapies, the beneficial effects of selective GR modulators are now being explored. Peroxisome proliferator-activated receptor-γ (PPARγ) agonism using thiazolidinediones has potent podocyte cytoprotective and nephroprotective effects. Repurposing of thiazolidinediones or identification of novel PPARγ modulators are potential strategies to treat non-diabetic glomerular disease. Retinoic acid receptor-α is the key mediator of the renal protective effects of retinoic acid, and repair of the endogenous retinoic acid pathway offers another potential therapeutic strategy for glomerular disease. Vitamin D receptor, oestrogen receptor and mineralocorticoid receptor modulators regulate podocyte injury in experimental models. Further studies are needed to better understand the mechanisms of these nuclear receptors, evaluate their synergistic pathways and identify their novel modulators. Here, we focus on the role of nuclear receptors in podocyte biology and non-diabetic glomerular disease.

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.

Use of computational toxicology (CompTox) tools to predict in vivo toxicity for risk assessment

Computational Toxicology tools were used to predict toxicity for three pesticides: propyzamide (PZ), carbaryl (CB) and chlorpyrifos (CPF). The tools used included: a) ToxCast/Tox21 assays (AC₅₀ s μM: concentration 50% maximum activity); b) in vitro-to-in vivo extrapolation (IVIVE) using ToxCast/Tox21 AC₅₀s to predict administered equivalent doses (AED: mg/kg/d) to compare to known in vivo Lowest-Observed-Effect-Level (LOEL)/Benchmark Dose (BMD); c) high throughput toxicokinetics population based (HTTK-Pop) using AC₅₀s for endpoints associated with the mode of action (MOA) to predict age-adjusted AED for comparison with in vivo LOEL/BMDs. ToxCast/Tox21 active-hit-calls for each chemical were predictive of targets associated with each MOA, however, assays directly relevant to the MOAs for each chemical were limited. IVIVE AEDs were predictive of in vivo LOEL/BMD₁₀s for all three pesticides. HTTK-Pop was predictive of in vivo LOEL/BMD₁₀s for PZ and CPF but not for CB after human age adjustments 11-15 (PZ) and 6-10 (CB) or 6-10 and 11-20 (CPF) corresponding to treated rat ages (in vivo endpoints). The predictions of computational tools are useful for risk assessment to identify targets in chemical MOAs and to support in vivo endpoints. Data can also aid is decisions about the need for further studies.

The PPAR Ω Pocket: Renewed Opportunities for Drug Development

The past decade of PPARγ research has dramatically improved our understanding of the structural and mechanistic bases for the diverging physiological effects of different classes of PPARγ ligands. The discoveries that lie at the heart of these developments have enabled the design of a new class of PPARγ ligands, capable of isolating central therapeutic effects of PPARγ modulation, while displaying markedly lower toxicities than previous generations of PPARγ ligands. This review examines the emerging framework around the design of these ligands and seeks to unite its principles with the development of new classes of ligands for PPARα and PPARβ/δ. The focus is on the relationships between the binding modes of ligands, their influence on PPAR posttranslational modifications, and gene expression patterns. Specifically, we encourage the design and study of ligands that primarily bind to the Ω pockets of PPARα and PPARβ/δ. In support of this development, we highlight already reported ligands that if studied in the context of this new framework may further our understanding of the gene programs regulated by PPARα and PPARβ/δ. Moreover, recently developed pharmacological tools that can be utilized in the search for ligands with new binding modes are also presented.

Peroxisome Proliferator-Activated Receptors: Experimental Targeting for the Treatment of Inflammatory Bowel Diseases

The peroxisome proliferator-activated receptors (PPARs) are a group of nuclear receptor proteins that promote ligand-dependent transcription of target genes that regulate energy production, lipid metabolism, and inflammation. The PPAR superfamily comprises three subtypes, PPARα, PPARγ, and PPARβ/δ, with differential tissue distributions. In addition to their different roles in the regulation of energy balance and carbohydrate and lipid metabolism, an emerging function of PPARs includes normal homeostasis of intestinal tissue. PPARα activation represses NF-κB signaling, which decreases the inflammatory cytokine production by different cell types, while PPARγ ligands can inhibit activation of macrophages and the production of inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, and Il-1β. In this regard, the anti-inflammatory responses induced by PPAR activation might restore physiopathological imbalances associated with inflammatory bowel diseases (IBD). Thus, PPARs and their ligands have important therapeutic potential. This review briefly discusses the roles of PPARs in the physiopathology and therapies of the most important IBDs, ulcerative colitis (UC), and Crohn's disease (CD), as well some new experimental compounds with PPAR activity as promising drugs for IBD treatment.

Changes in PGC-1α/SIRT1 Signaling Impact on Mitochondrial Homeostasis in Amyloid-Beta Peptide Toxicity Model

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive impairment that increasingly afflicts the elderly population. Soluble oligomers (AβOs) has been implicated in AD pathogenesis: however, the molecular events underlying a role for Aβ are not well understood. We studied the effects of AβOs on mitochondrial function and on key proteins that regulate mitochondrial dynamics and biogenesis in hippocampal neurons and PC-12 cells. We find that AβOs treatment caused a reduction in total Mfn1 after a 2 h exposure (42 ± 11%); while DRP1 increased at 1 and 2 h (205 ± 22% and 198 ± 27%, respectively), correlating to changes in mitochondrial morphology. We also observed that SIRT1 levels were reduced after acute and chronic AβOs treatment (68 ± 7% and 77 ± 6%, respectively); while PGC-1α levels were reduced with the same time treatments (68 ± 8% and 67 ± 7%, respectively). Interestingly, we found that chronic treatment with AβOs increased the levels of pSIRT1 (24 h: 157 ± 18%), and we observed changes in the PGC-1α and p-SIRT1 nucleus/cytosol ratio and SIRT1-PGC-1α interaction pattern after chronic exposure to AβOs. Our data suggest that AβOs induce important changes in the level and localization of mitochondrial proteins related with the loss of mitochondrial function that are mediated by a fast and sustained SIRT1/PGC-1α complex disruption promoting a “non-return point” to an irreversible synaptic failure and neuronal network disconnection.

Pharmacological (or Synthetic) and Nutritional Agonists of PPAR-γ as Candidates for Cytokine Storm Modulation in COVID-19 Disease

The cytokine storm is an abnormal production of inflammatory cytokines, due to the over-activation of the innate immune response. This mechanism has been recognized as a critical mediator of influenza-induced lung disease, and it could be pivotal for COVID-19 infections. Thus, an immunomodulatory approach targeting the over-production of cytokines could be proposed for viral aggressive pulmonary disease treatment. In this regard, the peroxisome proliferator-activated receptor (PPAR)-γ, a member of the PPAR transcription factor family, could represent a potential target. Beside the well-known regulatory role on lipid and glucose metabolism, PPAR-γ also represses the inflammatory process. Similarly, the PPAR-γ agonist thiazolidinediones (TZDs), like pioglitazone, are anti-inflammatory drugs with ameliorating effects on severe viral pneumonia. In addition to the pharmacological agonists, also nutritional ligands of PPAR-γ, like curcuma, lemongrass, and pomegranate, possess anti-inflammatory properties through PPAR-γ activation. Here, we review the main synthetic and nutritional PPAR-γ ligands, proposing a dual approach based on the strengthening of the immune system using pharmacological and dietary strategies as an attempt to prevent/treat cytokine storm in the case of coronavirus infection.

Dietary Fish Oil Concentrates Associated Health Benefits: A Recent Development of Cardiovascular Risk Reduction

Fish oil is an abundant source of omega-3 (n-3 or ω-3) polyunsaturated fatty acids (PUFAs) and contains Eicosapentaenoic Acid (EPA) and Docosahexaenoic Acid (DHA). PUFAs are very effective in preventing/ inhibiting cardiovascular incidents, particularly in individuals with high cardiovascular risk/accidents. In this review, composition, extraction of fish oil and its favorable/beneficial effects in Cardiovascular Diseases (CVDs) and molecular mechanism for its treatment/reduction have been discussed. Moreover, the application of fish oil for preventive/protective and remedial/curative properties in nutritive and health benefits has been summarized. All these aspects further search the opportunities/hope and scope with its expected opening and anticipations/ possibilities to provide additional therapeutic substitutes for the reduction of CVDs and registration of new drugs.

High-fat diet induces mouse liver steatosis with a concomitant decline in energy metabolism: attenuation by eicosapentaenoic acid (EPA) or hydroxytyrosol (HT) supplementation and the additive effects upon EPA and HT co-administration

High-fat-diet (HFD) feeding is associated with liver oxidative stress (OS), n-3 long-chain polyunsaturated fatty acid (n-3 LCPUFA) depletion, hepatic steatosis and mitochondrial dysfunction. Our hypothesis is that the HFD-induced liver injury can be attenuated by the combined supplementation of n-3 LCPUFA eicosapentaenoic acid (EPA) and the antioxidant hydroxytyrosol (HT). The C57BL/6J mice were administered an HFD (60% fat, 20% protein, 20% carbohydrates) or control diet (CD; 10% fat, 20% protein, 70% carbohydrates), with or without EPA (50 mg kg-1 day-1), HT (5 mg kg-1 day-1), or EPA + HT (50 and 5 mg kg-1 day-1, respectively) for 12 weeks. We measured the body and liver weights and dietary and energy intakes along with liver histology, FA composition, steatosis score and associated transcription factors, mitochondrial functions and metabolic factors related to energy sensing through the AMP-activated protein kinase (AMPK) and PPAR-γ coactivator-1α (PGC-1α) cascade. It was found that the HFD significantly induced liver steatosis, with a 66% depletion of n-3 LCPUFAs and a 100% increase in n-6/n-3 LCPUFA ratio as compared to the case of CD (p < 0.05). These changes were concomitant with (i) a 95% higher lipogenic and 70% lower FA oxidation signaling, (ii) a 40% diminution in mitochondrial respiratory capacity and (iii) a 56% lower ATP content. HFD-induced liver steatosis was also associated with (iv) a depressed mRNA expression of AMPK-PGC-1α signaling components, nuclear respiratory factor-2 (NRF-2) and β-ATP synthase. These HFD effects were significantly attenuated by the combined EPA + HT supplementation in an additive manner. These results suggested that EPA and HT co-administration partly prevented HFD-induced liver steatosis, thus strengthening the importance of combined interventions in hepatoprotection in non-alcoholic fatty liver disease.

Flow cytometry-based FRET identifies binding intensities in PPARγ1 protein-protein interactions in living cells

PPARγ is a pharmacological target in inflammatory and metabolic diseases. Upon agonistic treatment or following antagonism, binding of co-factors is altered, which consequently affects PPARγ-dependent transactivation as well as its DNA-independent properties. Therefore, establishing techniques to characterize these interactions is an important issue in living cells. Methods: Using the FRET pair Clover/mRuby2, we set up a flow cytometry-based FRET assay by analyzing PPARγ1 binding to its heterodimerization partner RXRα. Analyses of PPARγ-reporter and co-localization studies by laser-scanning microscopy validated this system. Refining the system, we created a new readout to distinguish strong from weak interactions, focusing on PPARγ-binding to the co-repressor N-CoR2. Results: We observed high FRET in cells expressing Clover-PPARγ1 and mRuby2-RXRα, but no FRET when cells express a mRuby2-RXRα deletion mutant, lacking the PPARγ interaction domain. Focusing on the co-repressor N-CoR2, we identified in HEK293T cells the new splice variant N-CoR2-ΔID1-exon. Overexpressing this isoform tagged with mRuby2, revealed no binding to Clover-PPARγ1, nor in murine J774A.1 macrophages. In HEK293T cells, binding was even lower in comparison to N-CoR2 constructs in which domains established to mediate interaction with PPARγ binding are deleted. These data suggest a possible role of N-CoR2-ΔID1-exon as a dominant negative variant. Because binding to N-CoR2-mRuby2 was not altered following activation or antagonism of Clover-PPARγ1, we determined the effect of pharmacological treatment on FRET intensity. Therefore, we calculated flow cytometry-based FRET efficiencies based on our flow cytometry data. As with PPARγ antagonism, PPARγ agonist treatment did not prevent binding of N-CoR2. Conclusion: Our system allows the close determination of protein-protein interactions with a special focus on binding intensity, allowing this system to characterize the role of protein domains as well as the effect of pharmacological agents on protein-protein interactions.

Transcriptomic study of the mechanism of anoikis resistance in head and neck squamous carcinoma

Background

Normal epithelial cells rapidly undergo apoptosis as soon as they lose contact with the extracellular matrix (ECM), which is termed as anoikis. However, cancer cells tend to develop a resistance mechanism to anoikis. This acquired ability is termed as anoikis resistance. Cancer cells, with anoikis resistance, can spread to distant tissues or organs via the peripheral circulatory system and cause cancer metastasis. Thus, inhibition of anoikis resistance blocks the metastatic ability of cancer cells.

Methods

Anoikis-resistant CAL27 (CAL27^AR) cells were induced from CAL27 cells using the suspension culture approach. Transcriptome analysis was performed using RNA-Seq to study the differentially expressed genes (DEGs) between the CAL27^ARcells and the parental CAL27 cells. Gene function annotation and Gene Ontology (GO) enrichment analysis were performed using DAVID database. Signaling pathways involved in DEGs were analyzed using Gene Set Enrichment Analysis (GSEA) software. Analysis results were confirmed by reverse transcription PCR (RT-PCR), western blotting, and gene correlation analysis based on the TCGA database.

Results

GO enrichment analysis indicated that the biological process (BP) of the DEGs was associated with epidermal development, DNA replication, and G1/S transition of the mitotic cell cycle. The analysis of cellular component (CC) showed that the most significant up-regulated genes were related to extracellular exosome. KEGG Pathway analysis revealed that 23 signaling pathways were activated (p-value ≤ 0.05, FDR q-value ≤ 0.05) and 22 signaling pathways were suppressed (p-value ≤ 0.05, FDR q-value ≤ 0.05). The results from the GSEA indicated that in contrast to the inhibition of EGFR signaling pathway, the VEGF signaling pathway was activated. The VEGF signaling pathway possibly activates STAT3 though induction of STAT3 phosphorylation. Gene correlation analysis revealed that the VEGFA- STAT3-KLF4-CDKN1A signal axis was not only present in head and neck squamous carcinoma (HNSCC) but also two other epithelial-derived carcinomas that highly express VEGFA, including kidney renal clear cell carcinoma (KIRC) and ovarian serous cystadenocarcinoma (OV).

RNase MCPIP1 regulates hepatic peroxisome proliferator-activated receptor gamma via TXNIP/PGC-1alpha pathway

Monocyte chemoattractant protein-1-induced protein-1 (MCPIP1) acts as an endonuclease that degrades selected mRNAs, viral RNAs and pre-miRNAs. MCPIP1 inhibits adipogenesis by degradation of C/EBPβ mRNA and adipogenesis-related miRNA, however its role in the regulation of hepatic lipid homeostasis is unknown. In this study, we investigated the role of MCPIP1 in the regulation of lipid metabolism in hepatocytes. C57BL/6 mice were fed a high-fat diet (HFD) for 2-20 weeks and next primary hepatocytes and adipose tissue were isolated. For in vitro experiments we used murine primary hepatocytes, control HepG2 cells and HepG2 with overexpressed or silenced MCPIP1. We found that Mcpip1 levels were lower in primary hepatocytes isolated from HFD-fed mice than in control cells starting at 4 weeks of a HFD. Level of Mcpip1 was also depleted in visceral fat isolated from obese and glucose-intolerant mice characterized by fatty liver disease. We showed that MCPIP1 overexpression in HepG2 cells treated with oleate induces the level and activity of peroxisome proliferator-activated receptor γ (PPARγ). This phenotype was reverted upon silencing of MCPIP1 in HepG2 cells and in primary hepatocytes lacking Mcpip1 protein. MCPIP1 activated the PPARγ transcription factor via the thioredoxin-interacting protein (TXNIP)/peroxisome proliferator-activated receptor γ coactivator 1- α (PGC-1α) pathway. MCPIP1 contributes to lipid metabolism in hepatocytes by regulating the TXNIP/PGC-1α/PPARγ pathway.

PPAR Ligands Containing Stilbene Scaffold

Peroxisome proliferator-activated receptors (PPARs) are transcriptional factors which belong to the ligand-activated nuclear receptor superfamily. They are ubiquitously expressed throughout the body. So far, three major subtypes have been identified, PPARα, PPARβ/δ and PPARγ. They are crucial for lipid and glucose metabolism and are also involved in the regulation of several types of tumors, inflammation, cardiovascular diseases and infertility. The importance of these transcription factors in physiology and pathophysiology has been largely investigated. Synthetic PPAR ligands are widely used in the treatment of dyslipidemia (e.g. fibrates - PPARα activators) or in diabetes mellitus (e.g. thiazolidinediones - PPARγ agonists) while a new generation of dual agonists reveals hypolipemic, hypotensive, antiatherogenic, anti-inflammatory and anticoagulant action. Many natural ligands, including polyphenolic compounds, influence the expression of these receptors. They have several health-promoting properties, including antioxidant, anti-inflammatory, and antineoplastic activities. Resveratrol, a stilbene polyphenol, is a biological active modulator of several signaling proteins, including PPARs. Given the enormous pharmacological potential of resveratrol, stilbene-based medicinal chemistry had a rapid increase covering various areas of research. The present review discusses ligands of PPARs that contain stilbene scaffold and summarises the different types of compounds on the basis of chemical structure.

Gemfibrozil, a Lipid-Lowering Drug, Lowers Amyloid Plaque Pathology and Enhances Memory in a Mouse Model of Alzheimer's Disease via Peroxisome Proliferator-Activated Receptor α

Deposition of extracellular senile plaques containing amyloid-β is one of the major neuropathological characteristics of Alzheimer’s disease (AD). Therefore, targeting amyloid-β dyshomeostasis is an important therapeutic strategy for treatment of AD. In this study, we demonstrate that gemfibrozil, an FDA-approved drug for hyperlipidemia, can lower the amyloid plaque burden in the hippocampus and cortex of the 5XFAD model of AD. Additionally, gemfibrozil reduced microgliosis and astrogliosis associated with plaque in these mice. Administration of gemfibrozil also improved spatial learning and memory of the 5XFAD mice. Finally, we delineate that gemfibrozil requires the transcription factor peroxisome proliferator-activated receptor alpha (PPARα) to exhibit its amyloid lowering and memory enhancing effects in 5XFAD mice. These results highlight a new therapeutic property of gemfibrozil and suggest that this drug may be repurposed for treatment of AD.

Do arachidonic acid metabolites affect apoptosis in bovine endometrial cells with silenced PPAR genes?

Peroxisome proliferator-activated receptors (PPARs) are expressed in bovine uterus, and their agonists are arachidonic acid (AA) metabolites. We hypothesised that silencing of PPAR genes in bovine endometrial stromal cells (ESC) would change the intracellular signalling through PPAR and affect apoptosis after cell treatment with different AA metabolites. The study's aims are detection of apoptosis and examining the influence of prostaglandins and leukotrienes on apoptosis occurring in physiological ESC and cells with silenced PPAR (α, δ, and γ) genes. Silencing the PPARα and PPARδ genes in cells resulted in increased DNA fragmentation and mRNA and protein expression of caspase (CASP) -3 and -8 (P < 0.05). Neither DNA fragmentation nor the mRNA and protein expression of CASP3 and -8 in cells with silenced PPARγ gene were changed compared to physiological cells (P > 0.05). Among PPARs, PPARα and PPARδ appear to inhibit apoptosis, and AA metabolites, as PPAR agonists, modify this process in bovine ESC.

Combined docosahexaenoic acid and thyroid hormone supplementation as a protocol supporting energy supply to precondition and afford protection against metabolic stress situations

Liver preconditioning (PC) refers to the development of an enhanced tolerance to injuring stimuli. For example, the protection from ischemia-reperfusion (IR) in the liver that is obtained by previous maneuvers triggering beneficial molecular and functional changes. Recently, we have assessed the PC effects of thyroid hormone (T_3; single dose of 0.1 mg/kg) and n-3 long-chain polyunsaturated fatty acids (n-3 LCPUFAs; daily doses of 450 mg/kg for 7 days) that abrogate IR injury to the liver. This feature is also achieved by a combined T₃ and the n-3 LCPUFA docosahexaenoic acid (DHA) using a reduced period of supplementation of the FA (daily doses of 300 mg/kg for 3 days) and half of the T₃ dosage (0.05 mg/kg). T₃ -dependent protective mechanisms include (i) the reactive oxygen species (ROS)-dependent activation of transcription factors nuclear factor-κB (NF-κB), AP-1, signal transducer and activator of transcription 3, and nuclear factor erythroid-2-related factor 2 (Nrf2) upregulating the expression of protective proteins. (ii) ROS-induced endoplasmic reticulum stress affording proper protein folding. (iii) The autophagy response to produce FAs for oxidation and ATP supply and amino acids for protein synthesis. (iv) Downregulation of inflammasome nucleotide-bonding oligomerization domain leucine-rich repeat containing family pyrin containing 3 and interleukin-1β expression to prevent inflammation. N-3 LCPUFAs induce antioxidant responses due to Nrf2 upregulation, with inflammation resolution being related to production of oxidation products and NF-κB downregulation. Energy supply to achieve liver PC is met by the combined DHA plus T₃ protocol through upregulation of AMPK coupled to peroxisome proliferator-activated receptor-γ coactivator 1α signaling. In conclusion, DHA plus T₃ coadministration favors hepatic bioenergetics and lipid homeostasis that is of crucial importance in acute and clinical conditions such as IR, which may be extended to long-term or chronic situations including steatosis in obesity and diabetes. © 2019 IUBMB Life, 71(9):1211-1220, 2019.

Docosahexaenoic acid-thyroid hormone combined protocol as a novel approach to metabolic stress disorders: Relation to mitochondrial adaptation via liver PGC-1α and sirtuin1 activation

Docosahexaenoic acid (DHA) and 3,3',5-triiodothyronine (T₃ ) combined protocol affords protection against liver injury via AMPK signaling supporting energy requirements. The aim of this work was to test the hypothesis that a DHA + T₃ accomplish mitochondrial adaptation through downstream upregulation of PPAR-γ coactivator 1α (PGC-1α). Male Sprague-Dawley rats were given daily oral doses of 300 mg DHA/kg or saline (controls) for three consecutive days, followed by 0.05 mg T₃ /kg (or hormone vehicle) ip at the fourth day, or single dose of 0.1 mg T₃ /kg alone. Liver mRNA levels were assayed by qPCR, NAD⁺ /NADH ratios, hepatic proteins, histone 3 acetylation and serum T₃ and β-hydroxybutyrate levels were determined by specific ELISA kits. Combined DHA + T₃ protocol led to increased liver AMPK, PGC-1α, NRF-2, COX-IV, and β-ATP synthase mRNAs, with concomitant higher protein levels of COX-IV and NRF-2, 369% enhancement in the NAD⁺ /NADH ratio, 47% decrease in histone 3 acetylation and 162% increase in serum levels of β-hydroxybutyrate over control values. These changes were reproduced by the higher dose of T₃ without major alterations by DHA or T₃ alone. In conclusion, liver mitochondrial adaptation by DHA + T₃ is associated with PGC-1α upregulation involving enhanced transcription of the coactivator, which may be contributed by PGC-1α deacetylation and phosphorylation by SIRT1 and AMPK activation, respectively. This contention is supported by NRF-2-dependent enhancement in COX-1 and β-ATP synthase induction with higher fatty acid oxidation resulting in a significant ketogenic response, which may represent a suitable strategy for hepatic steatosis with future clinical applications. © 2018 BioFactors, 45(2):271-278, 2019.

Risk to human health related to the presence of perfluorooctane sulfonic acid and perfluorooctanoic acid in food

The European Commission asked EFSA for a scientific evaluation on the risks to human health related to the presence of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in food. Regarding PFOS and PFOA occurrence, the final data set available for dietary exposure assessment contained a total of 20,019 analytical results (PFOS n = 10,191 and PFOA n = 9,828). There were large differences between upper and lower bound exposure due to analytical methods with insufficient sensitivity. The CONTAM Panel considered the lower bound estimates to be closer to true exposure levels. Important contributors to the lower bound mean chronic exposure were 'Fish and other seafood', 'Meat and meat products' and 'Eggs and egg products', for PFOS, and 'Milk and dairy products', 'Drinking water' and 'Fish and other seafood' for PFOA. PFOS and PFOA are readily absorbed in the gastrointestinal tract, excreted in urine and faeces, and do not undergo metabolism. Estimated human half-lives for PFOS and PFOA are about 5 years and 2-4 years, respectively. The derivation of a health-based guidance value was based on human epidemiological studies. For PFOS, the increase in serum total cholesterol in adults, and the decrease in antibody response at vaccination in children were identified as the critical effects. For PFOA, the increase in serum total cholesterol was the critical effect. Also reduced birth weight (for both compounds) and increased prevalence of high serum levels of the liver enzyme alanine aminotransferase (ALT) (for PFOA) were considered. After benchmark modelling of serum levels of PFOS and PFOA, and estimating the corresponding daily intakes, the CONTAM Panel established a tolerable weekly intake (TWI) of 13 ng/kg body weight (bw) per week for PFOS and 6 ng/kg bw per week for PFOA. For both compounds, exposure of a considerable proportion of the population exceeds the proposed TWIs.

Risk to human health related to the presence of perfluorooctane sulfonic acid and perfluorooctanoic acid in food

The European Commission asked EFSA for a scientific evaluation on the risks to human health related to the presence of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in food. Regarding PFOS and PFOA occurrence, the final data set available for dietary exposure assessment contained a total of 20,019 analytical results (PFOS n = 10,191 and PFOA n = 9,828). There were large differences between upper and lower bound exposure due to analytical methods with insufficient sensitivity. The CONTAM Panel considered the lower bound estimates to be closer to true exposure levels. Important contributors to the lower bound mean chronic exposure were 'Fish and other seafood', 'Meat and meat products' and 'Eggs and egg products', for PFOS, and 'Milk and dairy products', 'Drinking water' and 'Fish and other seafood' for PFOA. PFOS and PFOA are readily absorbed in the gastrointestinal tract, excreted in urine and faeces, and do not undergo metabolism. Estimated human half-lives for PFOS and PFOA are about 5 years and 2-4 years, respectively. The derivation of a health-based guidance value was based on human epidemiological studies. For PFOS, the increase in serum total cholesterol in adults, and the decrease in antibody response at vaccination in children were identified as the critical effects. For PFOA, the increase in serum total cholesterol was the critical effect. Also reduced birth weight (for both compounds) and increased prevalence of high serum levels of the liver enzyme alanine aminotransferase (ALT) (for PFOA) were considered. After benchmark modelling of serum levels of PFOS and PFOA, and estimating the corresponding daily intakes, the CONTAM Panel established a tolerable weekly intake (TWI) of 13 ng/kg body weight (bw) per week for PFOS and 6 ng/kg bw per week for PFOA. For both compounds, exposure of a considerable proportion of the population exceeds the proposed TWIs.

Protein Residue Networks from Energetic and Geometric Data: Are They Identical?

Protein residue networks (PRN) from energetic and geometric data are probably not identical. PRNs constructed from ab initio pair interaction energies are analyzed for the first time and compared to PRN based on center of mass separation. We use modern, previously unused algorithms such as global and local efficiencies to quantitatively confirm that both types of PRNs do exhibit small-world character. The main novelty finding is that interaction energy-based PRNs preserve small-world character even when clustered. A node hierarchy independent of the cutoff energy used for the edge creation is characteristic for them. Efficiency centrality identifies hubs responsible for such behavior. The interaction energy-based PRNs seem to comply with the scale-free network model with respect to efficiency centrality distribution as opposed to distance based PRNs. Community detection is introduced into protein network research as an extension beyond cluster analysis to study tertiary and quaternary structures.

The Role of PPAR-δ in Metabolism, Inflammation, and Cancer: Many Characters of a Critical Transcription Factor

Peroxisome proliferator-activated receptor-delta (PPAR-δ), one of three members of the PPAR group in the nuclear receptor superfamily, is a ligand-activated transcription factor. PPAR-δ regulates important cellular metabolic functions that contribute to maintaining energy balance. PPAR-δ is especially important in regulating fatty acid uptake, transport, and β-oxidation as well as insulin secretion and sensitivity. These salutary PPAR-δ functions in normal cells are thought to protect against metabolic-syndrome-related diseases, such as obesity, dyslipidemia, insulin resistance/type 2 diabetes, hepatosteatosis, and atherosclerosis. Given the high clinical burden these diseases pose, highly selective synthetic activating ligands of PPAR-δ were developed as potential preventive/therapeutic agents. Some of these compounds showed some efficacy in clinical trials focused on metabolic-syndrome-related conditions. However, the clinical development of PPAR-δ agonists was halted because various lines of evidence demonstrated that cancer cells upregulated PPAR-δ expression/activity as a defense mechanism against nutritional deprivation and energy stresses, improving their survival and promoting cancer progression. This review discusses the complex relationship between PPAR-δ in health and disease and highlights our current knowledge regarding the different roles that PPAR-δ plays in metabolism, inflammation, and cancer.

Signaling Mechanisms of Selective PPARγ Modulators in Alzheimer's Disease

Alzheimer's disease (AD) is a chronic neurodegenerative disease characterized by abnormal protein accumulation, synaptic dysfunction, and cognitive impairment. The continuous increase in the incidence of AD with the aged population and mortality rate indicates the urgent need for establishing novel molecular targets for therapeutic potential. Peroxisome proliferator-activated receptor gamma (PPARγ) agonists such as rosiglitazone and pioglitazone reduce amyloid and tau pathologies, inhibit neuroinflammation, and improve memory impairments in several rodent models and in humans with mild-to-moderate AD. However, these agonists display poor blood brain barrier permeability resulting in inadequate bioavailability in the brain and thus requiring high dosing with chronic time frames. Furthermore, these dosing levels are associated with several adverse effects including increased incidence of weight gain, liver abnormalities, and heart failure. Therefore, there is a need for identifying novel compounds which target PPARγ more selectively in the brain and could provide therapeutic benefits without a high incidence of adverse effects. This review focuses on how PPARγ agonists influence various pathologies in AD with emphasis on development of novel selective PPARγ modulators.

Molecular Actions of PPARα in Lipid Metabolism and Inflammation

Peroxisome proliferator-activated receptor α (PPARα) is a nuclear receptor of clinical interest as a drug target in various metabolic disorders. PPARα also exhibits marked anti-inflammatory capacities. The first-generation PPARα agonists, the fibrates, have however been hampered by drug-drug interaction issues, statin drop-in, and ill-designed cardiovascular intervention trials. Notwithstanding, understanding the molecular mechanisms by which PPARα works will enable control of its activities as a drug target for metabolic diseases with an underlying inflammatory component. Given its role in reshaping the immune system, the full potential of this nuclear receptor subtype as a versatile drug target with high plasticity becomes increasingly clear, and a novel generation of agonists may pave the way for novel fields of applications.

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

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

The influence of experimentally induced endometritis on the PPAR expression profile in the bovine endometrium

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors of the nuclear receptor superfamily. The PPARs activity can be modified e.g. by arachidonic acid metabolites. Escherichia coli (E. coli) is one of the main infectious agent of endometritis in dairy cows. We hypothesized that PPAR expression profile change in the bovine endometrium under the influence of LPS or E. coli. In experiment 1, endometrial explants were obtained post mortem from heifers and incubated without (control) or with LPS for 12, 24, 48, 72 and 96 h. In experiment 2, heifers were intrauterine infused with 0.9% NaCl (control) or with E. coli suspension in 0.9% NaCl. Endometrial biopsies were performed before (0 h) and 12, 24, 48, 72, 96 h after the infusions. In experiment 1, the increase in protein expression was observed for PPARα 48 h, for PPARβ/δ 24, 72 and 96 h, whereas for PPARγ 12, 24 and 96 h after LPS treatment relative to the control groups. In experiment 2, the up-regulation in protein expression was observed for PPARα 48 and 72 h, for PPARβ/δ 72 and 96 h, for PPARγ1 and PPARγ2 12 and 96 h after the intrauterine infusion with E. coli suspension compared to the control group. Changes in mRNA and protein PPAR expression profile in endometrial explants under the exposure of LPS indicate participation of these nuclear receptors in signal transduction during stimulation with LPS. The patterns of mRNA and protein PPAR expression in endometrial bioptates suggest that during experimentally induced endometritis in vivo, PPARs role may be connected both with enhancement of inflammation as well restoring physiological conditions in uterus.

The influence of arachidonic acid metabolites on PPAR and RXR expression in bovine uterine cells

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors belonging to the superfamily of nuclear receptors. Three isoforms have been described: alpha (PPARα), delta (PPARδ), and gamma (PPARγ). PPARs heterodimerize with retinoid X receptors (RXRs: RXRα, RXRβ and RXRγ). PPAR activity can be modulated by several ligands, including arachidonic acid (AA) metabolites. The aims of the study were to determine the effect of AA metabolites (prostaglandin [PG]E₂, PGF_2α, leukotriene [LT]B₄, and LTC₄) on mRNA (real-time PCR) and protein expression (Western blotting) of PPARα, PPARδ, and PPARγ, and on mRNA expression of RXRα, RXRβ, and RXRγ, in bovine epithelial, stromal, and myometrial primary uterine cells and in bovine stromal cells with silenced PPAR genes (N = 10). All PPAR and RXR isoforms were expressed. Prostaglandins affected expression of PPARs only in stromal cells, whereas LTs modulated PPARγ mRNA expression in epithelial and myometrial primary cells. Blockade of signal transduction through PPARs prevented interactions between AA metabolites and PPARs and changed RXR expression comparing with primary stromal cells. In primary stromal uterine cells, mRNA expression of RXRs was higher than that of PPARs. In uterine stromal cells in which intracellular signaling through PPARs was blocked, RXRs seem to take over the role of PPARs and are pivotal for cell functions. This study revealed the reaction of PPARs and RXRs to agonists which naturally occur in the bovine uterus.

Senescence Alters PPARγ (Peroxisome Proliferator–Activated Receptor Gamma)-Dependent Fatty Acid Handling in Human Adipose Tissue Microvascular Endothelial Cells and Favors Inflammation

Objective—

Adipose tissue (AT) dysfunction associated with obesity or aging is a major cause for lipid redistribution and the progression of cardiometabolic disorders. Our goal is to decipher the contribution of human AT microvascular endothelial cells (ECs) in the maintenance of fatty acid (FA) fluxes and the impact of senescence on their function.

Approach and Results—

We used freshly isolated primary microvascular ECs from human AT. Our data identified the endothelial FA handling machinery including FATPs (FA transport proteins) FATP1, FATP3, FATP4, and CD36 as well as FABP4 (FA binding protein 4). We showed that PPARγ (peroxisome proliferator–activated receptor gamma) regulates the expression of FATP1, CD36, and FABP4 and is a major regulator of FA uptake in human AT EC (hATEC). We provided evidence that endothelial PPARγ activity is modulated by senescence. Indeed, the positive regulation of FA transport by PPARγ agonist was abolished, whereas the emergence of an inflammatory response was favored in senescent hATEC. This was associated with the retention of nuclear FOXO1 (forkhead box protein O1), whereas nuclear PPARγ translocation was impaired.

Conclusions—

These data support the notion that PPARγ is a key regulator of primary hATEC function including FA handling and inflammatory response. However, the outcome of PPARγ activation is modulated by senescence, a phenomenon that may impact the ability of hATEC to properly respond to and handle lipid fluxes. Finally, our work highlights the role of hATEC in the regulation of FA fluxes and reveals that dysfunction of these cells with accelerated aging is likely to participate to AT dysfunction and the redistribution of lipids.

Research Advances in the Correlation between Peroxisome Proliferator-Activated Receptor-γ and Digestive Cancers

Peroxisome proliferator-activated receptor-γ (PPARγ) is a class of ligand-activated nuclear transcription factors, which is a member of type II nuclear receptor superfamily. Previous studies demonstrate that PPARγ is expressed in a variety of tumor tissues and is closely associated with the proliferation and prognosis of digestive system tumors by its roles in mediation of cell differentiation, induction of cell apoptosis, and inhibition of cell proliferation.

Correlation between PPAR-α methylation level in peripheral blood and inflammatory factors of NAFLD patients with DM

The correlation between the methylation levels of peroxisome proliferator-activated receptor-α (PPAR-α) in the peripheral blood and the inflammatory factors associated with non-alcoholic fatty liver disease (NAFLD) patients with diabetes mellitus (DM) was investigated. Thirty-two samples of normal liver tissues (group N) and 35 samples of liver tissues from NAFLD patients with DM (group M) were used for the present study. The levels of alanine transaminase (ALT) and aspartate transaminase (AST) were measured using commercially available kits. The accumulation of lipid droplets and glycogen in the two groups was determined through Oil Red O staining and Sudan III staining. mRNA expression of tumor necrosis factor-α (TNF-α), interleukin-lβ (IL-1β) and IL-6 in liver tissues of groups N and M were detected using reverse transcription-polymerase chain reaction (RT-PCR). In addition, western blotting was used to detect the protein expression of PPAR-α in liver tissues of both groups. The Statistical Product and Service Solutions (SPSS) 17.0 statistical software was used to analyze the expression difference of PPAR-α in liver tissues in the groups. The high levels of ALT and AST indicated severe liver injury in group M. Oil Red O staining and Sudan III staining showed a large number of lipid droplets and glycogen accumulation in the liver of group M patients. RT-PCR showed that the expression of inflammatory factors was extremely high and that the inflammatory injury was severe in the liver of group M patients. Western blotting showed that the expression of PPAR-α in group N was significantly higher than that in group M. ANOVA results showed that the expression of PPAR-α in liver tissues of groups N and M patients were statistically significantly different (P<0.01). Therefore, the abnormal expression of PPAR-α is closely associated with the occurrence and development of NAFLD complicated with DM, and that the abnormal expression of PPAR-α is closely related to inflammatory factors. Results from the present study suggest PPAR-α has important value in the study on NAFLD complicated with DM. The expression of PPAR-α can be used as a new basis for the diagnosis and treatment of NAFLD complicated with DM.

Anti-leukemic effects of PPARγ ligands

The peroxisome proliferator-activated receptor (PPAR) γ, a subtype of PPARs, is a member of the nuclear receptor family. PPARγ and its ligands contribute to various types of diseases including cancer. Given that currently developed therapies against leukemia are not very effective or safe, PPARγ ligands have been shown to be a new class of compounds with the potential to treat hematologic malignancies, particularly leukemia. The capability of PPARγ ligands to induce apoptosis, inhibit proliferation, and promote differentiation of leukemia cells suggests it has significant potential as a drug against leukemia. However, the specific mechanisms and molecules involved are not well-understood, although a number of PPARγ ligands with anti-leukemic effects have been identified. This may explain why PPARγ ligands have not been widely evaluated in clinical trials. To fill the gaps in the lack of understanding of specific anti-leukemic processes of PPARγ ligands and further adapt these molecules as anti-leukemic agents, this review describes previous studies of the anti-leukemic effects of PPARγ ligands.

Dose-dependent effects of peroxisome proliferator-activated receptors β/δ agonist on systemic inflammation after haemorrhagic shock

INTRODUCTION

PPARβ/δ agonists are known to modulate the systemic inflammatory response after sepsis. In this study, inflammation modulation effects of PPARβ/δ are investigated using the selective PPARβ/δ agonist (GW0742) in a model of haemorrhagic shock (HS)-induced sterile systemic inflammation.

METHODS

Blood pressure-controlled (35±5mmHg) HS was performed in C57/BL6 mice for 90min. Low-dose GW0742 (0.03mg/kg/BW) and high-dose GW0742 (0.3mg/kg/BW) were then administered at the beginning of resuscitation. Mice were sacrificed 6h after induction of HS. Plasma levels of IL-6, IL-1β, IL-10, TNFα, KC, MCP-1, and GM-CSF were determined by ELISA. Myeloperoxidase (MPO) activity in pulmonary and liver tissues was analysed with standardised MPO kits.

RESULTS

In mice treated with high-dose GW0742, plasma levels of IL-6, IL-1β, and MCP-1 were significantly increased compared to the control group mice. When compared to mice treated with low-dose GW0742 plasma levels of IL-6, IL-1β, GM-CSF, KC, and MCP-1 were significantly elevated in high-dose-treated mice. Low-dose GW0742 treatment was associated with a non-significant downtrend of inflammatory factors in mice with HS. No significant changes of MPO activity in lung and liver were observed between the control group and the GW0742 treatment groups.

CONCLUSION

This study identified dose-dependent effects of GW0742 on systemic inflammation after HS. While high-dose GW0742 substantially enhanced the systemic inflammatory response, low-dose GW0742 led to a downtrend of pro-inflammation cytokine expression. The exact mechanisms are yet unknown and need to be assessed in further studies.

Chiglitazar Preferentially Regulates Gene Expression via Configuration-Restricted Binding and Phosphorylation Inhibition of PPARγ

Type 2 diabetes mellitus is often treated with insulin-sensitizing drugs called thiazolidinediones (TZD), which improve insulin resistance and glycemic control. Despite their effectiveness in treating diabetes, these drugs provide little protection from eminent cardiovascular disease associated with diabetes. Here we demonstrate how chiglitazar, a configuration-restricted non-TZD peroxisome proliferator-activated receptor (PPAR) pan agonist with moderate transcription activity, preferentially regulates ANGPTL4 and PDK4, which are involved in glucose and lipid metabolism. CDK5-mediated phosphorylation at serine 273 (S273) is a unique regulatory mechanism reserved for PPARγ, and this event is linked to insulin resistance in type 2 diabetes mellitus. Our data demonstrates that chiglitazar modulates gene expression differently from two TZDs, rosiglitazone and pioglitazone, via its configuration-restricted binding and phosphorylation inhibition of PPARγ. Chiglitazar induced significantly greater expression of ANGPTL4 and PDK4 than rosiglitazone and pioglitazone in different cell models. These increased expressions were dependent on the phosphorylation status of PPARγ at S273. Furthermore, ChIP and AlphaScreen assays showed that phosphorylation at S273 inhibited promoter binding and cofactor recruitment by PPARγ. Based on these results, activities from pan agonist chiglitazar can be an effective part of a long-term therapeutic strategy for treating type 2 diabetes in a more balanced action among its targeted organs.

Mediator 1 Is Atherosclerosis Protective by Regulating Macrophage Polarization

OBJECTIVE

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

APPROACH AND RESULTS

To study the molecular mechanism by which MED1 regulates the M1/M2 phenotype switch of macrophage and the effect on atherosclerosis, we generated MED1/apolipoprotein E (ApoE) double-deficient (MED1ΔMac/ApoE-/-) mice and found that atherosclerosis was greater in MED1ΔMac/ApoE-/- mice than in MED1fl/fl/ApoE-/- littermates. The gene expression of M1 markers was increased and that of M2 markers decreased in both aortic wall and peritoneal macrophages from MED1ΔMac/ApoE-/- mice, whereas MED1 overexpression rectified the changes in M1/M2 expression. Moreover, LDLR (low-density lipoprotein receptor)-deficient mice received bone marrow from MED1ΔMac mice showed greater atherosclerosis. Mechanistically, MED1 ablation decreased the binding of PPARγ (peroxisome proliferator-activated receptor γ) and enrichment of H3K4me1 and H3K27ac to upstream region of M2 marker genes. Furthermore, interleukin 4 induction of PPARγ and MED1 increased the binding of PPARγ or MED1 to the PPAR response elements of M2 marker genes.

CONCLUSIONS

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

Targeting Peroxisome Proliferator-Activated Receptors Using Thiazolidinediones: Strategy for Design of Novel Antidiabetic Drugs

Thiazolidinediones are a class of well-established antidiabetic drugs, also named as glitazones. Thiazolidinedione structure has been an important structural domain of research, involving design and development of new drugs for the treatment of type 2 diabetes. Extensive research on the mechanism of action and the structural requirements has revealed that the intended antidiabetic activity in type 2 diabetes is due to their agonistic effect on peroxisome proliferator-activated receptor (PPAR) belonging to the nuclear receptor super family. Glitazones have specific affinity to PPARγ, one of the subtypes of PPARs. Certain compounds under development have dual PPARα/γ agonistic activity which might be beneficial in obesity and diabetic cardiomyopathy. Interesting array of hybrid compounds of thiazolidinedione PPARγ agonists exhibited therapeutic potential beyond antidiabetic activity. Pharmacology and chemistry of thiazolidinediones as PPARγ agonists and the potential of newer analogues as dual agonists of PPARs and other emerging targets for the therapy of type 2 diabetes are presented. This review highlights the possible modifications of the structural components in the general frame work of thiazolidinediones with respect to their binding efficacy, potency, and selectivity which would guide the future research in design of novel thiazolidinedione derivatives for the management of type 2 diabetes.

Astragaloside IV alleviates heart failure via activating PPARα to switch glycolysis to fatty acid β-oxidation

In heart failure (HF), energy metabolism pathway in cardiac muscle changes from fatty acid β-oxidation to glycolysis. However, the exact mechanism is unknown. Sarcoendoplasmic reticulum Ca²⁺α ATPase (SERCA) expression is downregulated and mitochondrial function is reduced in HF, perhaps partly due to a substantially reduced energy supply for excitation–contraction coupling resulting from a lower fatty acid β-oxidation rate. We investigated whether Astragaloside IV can activate peroxisome proliferator-activated receptor alpha (PPARα) to stimulate fatty acid β-oxidation and increase cardiac energy production, improving mitochondrial function and the efficiency of SERCA in HF. In pressure overload-induced HF mice and isolated hypertrophic myocardial cells, fatty acid β-oxidation and heart function were substantially strengthened following Astragaloside IV treatment, as demonstrated by the increased expression of PPARα and SERCA2a. In vitro, Astragaloside IV regulated energy metabolism by increasing ATP production and enhancing mitochondrial function, attributable to increased oxygen consumption and slightly increased mitochondrial Ca²⁺ uptake. In HF, Astragaloside IV switched glycolysis to fatty acid β-oxidation, as confirmed by reduced anaerobic glycolysis and an increased oxygen consumption ratio. These results suggest that Astragaloside IV can stimulate fatty acid β-oxidation and improve mitochondrial function, which may present a novel cardioprotective treatment that inhibits the progress of HF.

The Peroxisome-Mitochondria Connection: How and Why?

Over the past decades, peroxisomes have emerged as key regulators in overall cellular lipid and reactive oxygen species metabolism. In mammals, these organelles have also been recognized as important hubs in redox-, lipid-, inflammatory-, and innate immune-signaling networks. To exert these activities, peroxisomes must interact both functionally and physically with other cell organelles. This review provides a comprehensive look of what is currently known about the interconnectivity between peroxisomes and mitochondria within mammalian cells. We first outline how peroxisomal and mitochondrial abundance are controlled by common sets of cis- and trans-acting factors. Next, we discuss how peroxisomes and mitochondria may communicate with each other at the molecular level. In addition, we reflect on how these organelles cooperate in various metabolic and signaling pathways. Finally, we address why peroxisomes and mitochondria have to maintain a healthy relationship and why defects in one organelle may cause dysfunction in the other. Gaining a better insight into these issues is pivotal to understanding how these organelles function in their environment, both in health and disease.

PPARs: regulators of metabolism and as therapeutic targets in cardiovascular disease. Part II: PPAR-β/δ and PPAR-γ

The PPARs are a subfamily of three ligand-inducible transcription factors, which belong to the superfamily of nuclear hormone receptors. In mammals, the PPAR subfamily consists of three members: PPAR-α, PPAR-β/δ and PPAR-γ. PPARs control the expression of a large number of genes involved in metabolic homeostasis, lipid, glucose and energy metabolism, adipogenesis and inflammation. PPARs regulate a large number of metabolic pathways that are implicated in the pathogenesis of metabolic diseases such as metabolic syndrome, Type 2 diabetes mellitus, nonalcoholic fatty liver disease and cardiovascular disease. The aim of this review is to provide up-to-date information about the biochemical and metabolic actions of PPAR-β/δ and PPAR-γ, the therapeutic potential of their agonists currently under clinical development and the cardiovascular disease outcome of clinical trials of PPAR-γ agonists, pioglitazone and rosiglitazone.

PPARs: regulators of metabolism and as therapeutic targets in cardiovascular disease. Part I: PPAR-α

This article provides a comprehensive review about the molecular and metabolic actions of PPAR-α. It describes its structural features, ligand specificity, gene transcription mechanisms, functional characteristics and target genes. In addition, recent progress with the use of loss of function and gain of function mouse models in the discovery of diverse biological functions of PPAR-α, particularly in the vascular system and the status of the development of new single, dual, pan and partial PPAR agonists (PPAR modulators) in the clinical management of metabolic diseases are presented. This review also summarizes the clinical outcomes from a large number of clinical trials aimed at evaluating the atheroprotective actions of current clinically used PPAR-α agonists, fibrates and statin-fibrate combination therapy.

The many ways tissue phagocytes respond to dying cells

Apoptosis is an important component of normal tissue physiology, and the prompt removal of apoptotic cells is equally essential to avoid the undesirable consequences of their accumulation and disintegration. Professional phagocytes are highly specialized for engulfing apoptotic cells. The recent ability to track cells that have undergone apoptosis in situ has revealed a division of labor among the tissue resident phagocytes that sample them. Macrophages are uniquely programmed to process internalized apoptotic cell-derived fatty acids, cholesterol and nucleotides, as a reflection of their dominant role in clearing the bulk of apoptotic cells. Dendritic cells carry apoptotic cells to lymph nodes where they signal the emergence and expansion of highly suppressive regulatory CD4 T cells. A broad suppression of inflammation is executed through distinct phagocyte-specific mechanisms. A clever induction of negative regulatory nodes is notable in dendritic cells serving to simultaneously shut down multiple pathways of inflammation. Several of the genes and pathways modulated in phagocytes in response to apoptotic cells have been linked to chronic inflammatory and autoimmune diseases such as atherosclerosis, inflammatory bowel disease and systemic lupus erythematosus. Our collective understanding of old and new phagocyte functions after apoptotic cell phagocytosis demonstrates the enormity of ways to mediate immune suppression and enforce tissue homeostasis.