Modulation of PPAR activity via phosphorylation

The Role of Peroxisome Proliferator–Activated Receptor Gamma (PPARγ) in Mono(2-ethylhexyl) Phthalate (MEHP)-Mediated Cytotrophoblast Differentiation

BACKGROUND

Phthalates are environmental contaminants commonly used as plasticizers in polyvinyl chloride (PVC) products. Recently, exposure to phthalates has been associated with preterm birth, low birth weight, and pregnancy loss. There is limited information about the possible mechanisms linking maternal phthalate exposure and placental development, but one such mechanism may be mediated by peroxisome proliferator–activated receptor γ (PPARγ). PPARγ belongs to the nuclear receptor superfamily that regulates, in a ligand-dependent manner, the transcription of target genes. Studies of PPARγ-deficient mice have demonstrated its essential role in lipid metabolism and placental development. In the human placenta, PPARγ is expressed in the villous cytotrophoblast (VCT) and is activated during its differentiation into syncytiotrophoblast.

OBJECTIVES

The goal of this study was to investigate the action of mono(2-ethylhexyl) phthalate (MEHP) on PPARγ activity during in vitro differentiation of VCTs.

METHODS

We combined immunofluorescence, PPARγ activity/hCG assays, western blotting, and lipidomics analyses to characterize the impacts of physiologically relevant concentrations of MEHP (0.1, 1, and 10 μM) on cultured VCTs isolated from human term placentas.

RESULTS

Doses of 0.1 and 1 μM MEHP showed significantly lower PPARγ activity and less VCT differentiation in comparison with controls, whereas, surprisingly, a 10 μM dose had the opposite effect. MEHP exposure inhibited hCG production and significantly altered lipid composition. In addition, MEHP had significant effects on the mitogen-activated protein kinase (MAPK) pathway.

CONCLUSIONS

This study suggests that MEHP has a U-shaped dose–response effect on trophoblast differentiation that is mediated by the PPARγ pathway and acts as an endocrine disruptor in the human placenta. https://doi.org/10.1289/EHP3730.

Statins decrease leptin expression in human white adipocytes

Statin use is associated with increased calorie intake and consequent weight gain. It is speculated that statin‐dependent improvements in lipid profile may undermine the perceived need to follow lipid‐lowering and other dietary recommendations leading consequently to increased calorie intake. However, increases in calorie intake in statin users may also be related to statin‐dependent decreases in satiety factors such as leptin, an adipocyte‐derived adipokine. The objective of our study was to examine the direct effects of statins on leptin expression. Adipocytes are the main source of circulating leptin. Therefore, we examined the effects of atorvastatin and simvastatin on leptin expression in cultured human white adipocytes. We show that treatment of white adipocytes with simvastatin and atorvastatin decreases leptin mRNA expression (simvastatin: P = 0.008, atorvastatin: P = 0.03) and leptin secretion (simvastatin: P = 0.0001, atorvastatin: P = 0.0001). Both simvastatin and atorvastatin mediate decreases in leptin expression via extracellular‐signal‐regulated kinases 1/2 and peroxisome proliferator‐activated receptor gamma pathways (simvastatin: P = 0.01, atorvastatin: P = 0.026). Additionally, statin treatment also induced expected increases in adiponectin, while decreasing monocyte chemoattractant protein 1 (MCP1) mRNA. Furthermore, statins increased secretion of both total as well as high molecular weight adiponectin while decreasing MCP1 secretion. To conclude, statins act directly on human white adipocytes to regulate adipokine secretion and decrease leptin expression. Leptin is an important satiety factor. Hence, statin‐dependent decreases in leptin may contribute, at least in part, to increases in food intake in statin users.

Role of AMPK and PPARα in the anti-skin cancer effects of ursolic acid

The phytonutrient ursolic acid (UA), present in apples, rosemary, and other plant sources, has anti-cancer properties in a number of systems, including skin cancers. However, few reports have examined upstream mechanisms by which UA may prevent or treat cancer. Recent reports have indicated UA induces death of cancer cell lines via AMP-activated protein kinase (AMPK), an energy-sensing kinase which possesses both pro-metabolic and anti-cancer effects. Other studies have shown UA activates peroxisome proliferator activated receptor α (PPARα) and the glucocorticoid receptor (GR). Here, we found the cytotoxic effect of UA in skin carcinoma cells required AMPK activation. In addition, two inhibitors of PPARα partially reversed the cytotoxic effects of UA, suggesting its effects are at least partially mediated through this receptor. Finally, inhibition of the GR did not reverse the effects of UA nor did this compound bind the GR under the conditions of experiments performed. Overall, studies elucidating the anti-cancer effects of UA may allow for the development of more potent analogues utilizing similar mechanisms. These studies may also reveal the mediators of any possible side effects or resistance mechanisms to UA therapy.

3,5-Dicaffeoyl-Epi-Quinic Acid Isolated from Edible Halophyte Atriplex gmelinii Inhibits Adipogenesis via AMPK/MAPK Pathway in 3T3-L1 Adipocytes

Atriplex gmelinii is an edible halophyte that has been suggested to possess various health benefits. In the present study, 3,5-dicaffeoyl-epi-quinic acid (DEQA) isolated from A. gmelinii was tested for its ability to prevent adipogenesis in 3T3-L1 cells. Also, the molecular mechanisms by which DEQA affects differentiation of 3T3-L1 cells were investigated. The introduction of DEQA to differentiating 3T3-L1 preadipocytes resulted in suppressed adipogenesis and lowered expression of adipogenesis-related factors, PPARγ, C/EBPα, and SREBP-1c. Treatment of 3T3-L1 adipocytes with DEQA notably decreased the levels of phosphorylated p38, ERK, and JNK. In addition, presence of DEQA upregulated the levels of both inactive and phosphorylated adenosine monophosphate-activated protein kinase (AMPK) and its substrate, acetyl-CoA carboxylase (ACC). Taken together, current results indicated that DEQA exhibited a significant antiadipogenesis activity by activation of AMPK and downregulation of MAPK signal pathways in 3T3-L1 preadipocytes.

Elucidating the Beneficial Role of PPAR Agonists in Cardiac Diseases

Peroxisome proliferator-activated receptors (PPARs) are nuclear hormone receptors that bind to DNA and regulate transcription of genes involved in lipid and glucose metabolism. A growing number of studies provide strong evidence that PPARs are the promising pharmacological targets for therapeutic intervention in various diseases including cardiovascular disorders caused by compromised energy metabolism. PPAR agonists have been widely used for decades as lipid-lowering and anti-inflammatory drugs. Existing studies are mainly focused on the anti-atherosclerotic effects of PPAR agonists; however, their role in the maintenance of cellular bioenergetics remains unclear. Recent studies on animal models and patients suggest that PPAR agonists can normalize lipid metabolism by stimulating fatty acid oxidation. These studies indicate the importance of elucidation of PPAR agonists as potential pharmacological agents for protection of the heart from energy deprivation. Here, we summarize and provide a comprehensive analysis of previous studies on the role of PPARs in the heart under normal and pathological conditions. In addition, the review discusses the PPARs as a therapeutic target and the beneficial effects of PPAR agonists, particularly bezafibrate, to attenuate cardiomyopathy and heart failure in patients and animal models.

Haem oxygenase-1 up-regulation by rosiglitazone via ROS-dependent Nrf2-antioxidant response elements axis or PPARγ attenuates LPS-mediated lung inflammation

BACKGROUND AND PURPOSE

Haem oxygenase-1 (HO-1) is induced by thiazolidinediones including rosiglitazone and exerts anti-inflammatory effects in various models. However, the molecular mechanisms underlying rosiglitazone-induced HO-1 expression remain largely unknown in human pulmonary alveolar epithelial cells (HPAEpiCs).

EXPERIMENTAL APPROACH

HO-1 expression was determined by real time-PCR, Western blotting and promoter reporter analyses. Signalling pathways were investigated using pharmacological inhibitors or specific siRNAs. Interactions between nuclear factor erythroid-2-related factor (Nrf2) and antioxidant response elements (ARE) binding site of the HO-1 promoter were investigated with chromatin immunoprecipitation assays.

KEY RESULTS

Up-regulation of HO-1 in HPAEpiCs or in mice by rosiglitazone blunted ICAM-1 expression and monocyte adhesion to HPAEpiCs challenged with LPS. Rosiglitazone-induced HO-1 expression was significantly attenuated by NADPH oxidase (NOX) inhibitors (apocynin and diphenyleneiodonium) or ROS scavenger (N-acetyl cysteine). The involvement of NOX activity and ROS generation in rosiglitazone-induced HO-1 expression was confirmed by transfection with p47phox or NOX2 siRNA. Moreover, pretreatment with the inhibitors of c-Src (c-Srci II), proline-rich tyrosine kinase 2 (Pyk2) (PF431396), Akt (Akti VIII) or PPARγ (GW9662) and transfection with siRNA of c-Src, Pyk2, Akt or PPARγ abolished the rosiglitazone-induced HO-1 expression in HPAEpiCs. Subsequently, Nrf2 was activated by phosphorylation of c-Src, Pyk2 and Akt, which turned on transcription of HO-1 gene by binding to AREs binding site and enhancing ARE promoter activity.

CONCLUSIONS AND IMPLICATIONS

Rosiglitazone induces HO-1 expression via either NOX/ROS/c-Src/Pyk2/Akt-dependent Nrf2 activation or PPARγ in HPAEpiCs and suppresses LPS-mediated inflammatory responses, suggesting that PPARγ agonists may be useful for protection against pulmonary inflammation.

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.

Peroxisome Proliferator-Activated Receptor gamma negatively regulates liver regeneration after partial hepatectomy via the HGF/c-Met/ERK1/2 pathways

Peroxisome Proliferator-Activated Receptor gamma (PPARγ) is a nuclear receptor demonstrated to play an important role in various biological processes. The aim of this study was to determine the effect of PPARγ on liver regeneration upon partial hepatectomy (PH) in mice. Mice were subjected to two-thirds PH. Before surgery, mice were either treated with the PPARγ agonist rosiglitazone, the PPARγ antagonist GW9662 alone, or with the c-met inhibitor SGX523. Liver-to-body-weight ratio, lab values, and proliferation markers were assessed. Components of the PPARγ-specific signaling pathway were identified by western blot and qRT-PCR. Our results show that liver regeneration is being inhibited by rosiglitazone and accelerated by GW9662. Inhibition of c-Met by SGX523 treatment abrogates GW9662-induced liver regeneration and hepatocyte proliferation. Hepatocyte growth factor (HGF) protein levels were significantly downregulated after rosiglitazone treatment. Activation of HGF/c-Met pathways by phosphorylation of c-Met and ERK1/2 were inhibited in rosiglitazone-treated mice. In turn, blocking phosphorylation of c-Met significantly abrogated the augmented effect of GW9662 on liver regeneration. Our data support the concept that PPARγ abrogates liver growth and hepatocellular proliferation by inhibition of the HGF/c-Met/ERK1/2 pathways. These pathways may represent potential targets in response to liver disease and could impact on the development of molecular therapies.

Morus alba Leaf Bioactives Modulate Peroxisome Proliferator Activated Receptor γ in the Kidney of Diabetic Rat and Impart Beneficial Effect

Peroxisome proliferator activated receptor gamma (PPARγ) is a ligand-activated nuclear receptor that can be activated or repressed by several exogenous and endogenous ligands and acts by modulating genes that regulate lipid, glucose, and insulin homeostasis. In kidney, PPARγ is involved in normal kidney development and other physiological functions. In our earlier report, we showed that feeding Morus alba leaves to experimental diabetic rats ameliorated diabetic nephropathy and significantly decreased microalbuminuria. In this paper, we have attempted to look into the molecular mechanism involving PPARγ modulation by mulberry leaf bioactive compounds by in vitro and in vivo methods and its impact on key inflammatory markers. In vitro assay by TR-FRET suggested that mulberry leaf extracts can serve as a putative modulator of PPARγ. High glucose conditions in vitro and in vivo increased PPARγ levels, which were ameliorated by mulberry leaves or their extracts. Interestingly, PPARγ was significantly phosphorylated at Ser112 by upstream kinases ERK42/44 in kidney of diabetic animals on feeding mulberry leaves. In vitro studies using MDCK cell line revealed that increased Ser112 phosphorylation was observed when cells were treated with bound phenolic acid rich extract but not with free phenolic acid rich extracts. HPLC analysis and bioassay-guided activity revealed that coumaric acid was the bioactive molecule within bound phenolic acid rich extract that was responsible for increased ERK42/44-mediated phosphorylation at Ser112. Furthermore, mulberry leaf bioactive compounds showed beneficial effect on the tested inflammatory markers.

Diverse roles of fatty acid binding proteins (FABPs) in development and pathogenesis of cancers

One of the most importantly involved pathways in cancer development is fatty-acid signaling pathway. Synthesized lipids as energetic sources are consumed by cancer cells for proliferation, growth, survival, invasion and angiogenesis. Fatty acids as signaling compounds regulate metabolic and transcriptional networks, survival pathways and inflammatory responses. Aggregation of fatty acids with fatty acid binding proteins (FABPs) facilitates their transportation to different cell organelles. FABPs, a group of lipid binding proteins modulate fatty acid metabolism, cell growth and proliferation and cancer development. They may be used as tumor marker in some cancers. FABPs are expressed in most malignancies such as prostate, breast, liver, bladder and lung cancer which are associated with the incidence, proliferation, metastasis, invasion of tumors. This review introduces several isoforms of FABPs (FABP1-12) and summarizes their function and their possible roles in cancer development through some proposed mechanisms.

Maintenance of Kidney Metabolic Homeostasis by PPAR Gamma

Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear hormone receptors that control the transcription of specific genes by binding to regulatory DNA sequences. Among the three subtypes of PPARs, PPARγ modulates a broad range of physiopathological processes, including lipid metabolism, insulin sensitization, cellular differentiation, and cancer. Although predominantly expressed in adipose tissue, PPARγ expression is also found in different regions of the kidney and, upon activation, can redirect metabolism. Recent studies have highlighted important roles for PPARγ in kidney metabolism, such as lipid and glucose metabolism and renal mineral control. PPARγ is also implicated in the renin-angiotensin-aldosterone system and, consequently, in the control of systemic blood pressure. Accordingly, synthetic agonists of PPARγ have reno-protective effects both in diabetic and nondiabetic patients. This review focuses on the role of PPARγ in renal metabolism as a likely key factor in the maintenance of systemic homeostasis.

A collagen domain-derived short adiponectin peptide activates APPL1 and AMPK signaling pathways and improves glucose and fatty acid metabolisms

Adiponectin is a fat tissue-derived adipokine with beneficial effects against diabetes, cardiovascular diseases, and cancer. Accordingly, adiponectin-mimetic molecules possess significant pharmacological potential. Oligomeric states of adiponectin appear to determine its biological activity. We identified a highly conserved, 13-residue segment (ADP-1) from adiponectin's collagen domain, which comprises GXXG motifs and has one asparagine and two histidine residues that assist in oligomeric protein assembly. We therefore hypothesized that ADP-1 promotes oligomeric assembly and thereby mediates potential metabolic effects. We observed here that ADP-1 is stable in human serum and oligomerizes in aqueous environments. We also found that ADP-1 activates AMP-activated protein kinase (AMPK) in an adaptor protein, phosphotyrosine interacting with PH domain and leucine zipper 1 (APPL1)-dependent pathway and stimulates glucose uptake in rat skeletal muscle cells (L6 myotubes). ADP-1-induced glucose transport coincided with ADP-1-induced biosynthesis of glucose transporter 4 and its translocation to the plasma membrane. ADP-1 induced an interaction between APPL1 and the small GTPase Rab5, resulting in AMPK phosphorylation, in turn leading to phosphorylation of p38 mitogen-activated protein kinase (MAPK), acetyl-CoA carboxylase, and peroxisome proliferator-activated receptor α. Similar to adiponectin, ADP-1 increased the expression of the adiponectin receptor 1 (AdipoR1) gene. Of note, ADP-1 decreased blood glucose levels and enhanced insulin production in pancreatic β cells in db/db mice. Further, ADP-1 beneficially affected lipid metabolism by enhancing lipid globule formation in mouse 3T3-L1 adipocytes. To our knowledge, this is the first report on identification of a short peptide from adiponectin with positive effects on glucose or fatty acid metabolism.

NHR-49/HNF4 integrates regulation of fatty acid metabolism with a protective transcriptional response to oxidative stress and fasting

Endogenous and exogenous stresses elicit transcriptional responses that limit damage and promote cell/organismal survival. Like its mammalian counterparts, hepatocyte nuclear factor 4 (HNF4) and peroxisome proliferator-activated receptor α (PPARα), Caenorhabditis elegans NHR-49 is a well-established regulator of lipid metabolism. Here, we reveal that NHR-49 is essential to activate a transcriptional response common to organic peroxide and fasting, which includes the pro-longevity gene fmo-2/flavin-containing monooxygenase. These NHR-49-dependent, stress-responsive genes are also upregulated in long-lived glp-1/notch receptor mutants, with two of them making critical contributions to the oxidative stress resistance of wild-type and long-lived glp-1 mutants worms. Similar to its role in lipid metabolism, NHR-49 requires the mediator subunit mdt-15 to promote stress-induced gene expression. However, NHR-49 acts independently from the transcription factor hlh-30/TFEB that also promotes fmo-2 expression. We show that activation of the p38 MAPK, PMK-1, which is important for adaptation to a variety of stresses, is also important for peroxide-induced expression of a subset of NHR-49-dependent genes that includes fmo-2. However, organic peroxide increases NHR-49 protein levels, by a posttranscriptional mechanism that does not require PMK-1 activation. Together, these findings establish a new role for the HNF4/PPARα-related NHR-49 as a stress-activated regulator of cytoprotective gene expression.

Biliverdin reductase and bilirubin in hepatic disease

The buildup of fat in the liver (hepatic steatosis) is the first step in a series of incidents that may drive hepatic disease. Obesity is the leading cause of nonalcoholic fatty liver disease (NAFLD), in which hepatic steatosis progresses to liver disease. Chronic alcohol exposure also induces fat accumulation in the liver and shares numerous similarities to obesity-induced NAFLD. Regardless of whether hepatic steatosis is due to obesity or long-term alcohol use, it still may lead to hepatic fibrosis, cirrhosis, or possibly hepatocellular carcinoma. The antioxidant bilirubin and the enzyme that generates it, biliverdin reductase A (BVRA), are components of the heme catabolic pathway that have been shown to reduce hepatic steatosis. This review discusses the roles for bilirubin and BVRA in the prevention of steatosis, their functions in the later stages of liver disease, and their potential therapeutic application.

Saccharomyces cerevisiae Boulardii Reduces the Deoxynivalenol-Induced Alteration of the Intestinal Transcriptome

Type B trichothecene mycotoxin deoxynivalenol (DON) is one of the most frequently occurring food contaminants. By inducing trans-activation of a number of pro-inflammatory cytokines and increasing the stability of their mRNA, trichothecene can impair intestinal health. Several yeast products, especially Saccharomyces cerevisiae, have the potential for improving the enteric health of piglets, but little is known about the mechanisms by which the administration of yeast counteracts the DON-induced intestinal alterations. Using a pig jejunum explant model, a whole-transcriptome analysis was performed to decipher the early response of the small intestine to the deleterious effects of DON after administration of S. cerevisiae boulardii strain CNCM I-1079. Compared to the control condition, no differentially expressed gene (DE) was observed after treatment by yeast only. By contrast, 3619 probes-corresponding to 2771 genes-were differentially expressed following exposure to DON, and 32 signaling pathways were identified from the IPA software functional analysis of the set of DE genes. When the intestinal explants were treated with S. cerevisiae boulardii prior to DON exposure, the number of DE genes decreased by half (1718 probes corresponding to 1384 genes). Prototypical inflammation signaling pathways triggered by DON, including NF-κB and p38 MAPK, were reversed, although the yeast demonstrated limited efficacy toward some other pathways. S. cerevisiae boulardii also restored the lipid metabolism signaling pathway, and reversed the down-regulation of the antioxidant action of vitamin C signaling pathway. The latter effect could reduce the burden of DON-induced oxidative stress. Altogether, the results show that S. cerevisiae boulardii reduces the DON-induced alteration of intestinal transcriptome, and point to new mechanisms for the healing of tissue injury by yeast.

Modulation of Nuclear Receptor Function by Chromatin Modifying Factor TIP60

Nuclear receptors (NRs) are transcription factors that bind to specific DNA sequences known as hormone response elements located upstream of their target genes. Transcriptional activity of NRs can be modulated by binding of the compatible ligand and transient interaction with cellular coregulators, functioning either as coactivators or as corepressors. Many coactivator proteins possess intrinsic histone acetyltransferase (HAT) activity that catalyzes the acetylation of specific lysine residues in histone tails and loosens the histone-DNA interaction, thereby facilitating access of transcriptional factors to the regulatory sequences of the DNA. Tat interactive protein 60 (TIP60), a member of the Mof-Ybf2-Sas2-TIP60 family of HAT protein, is a multifunctional coregulator that controls a number of physiological processes including apoptosis, DNA damage repair, and transcriptional regulation. Over the last two decades or so, TIP60 has been extensively studied for its role as NR coregulator, controlling various aspect of steroid receptor functions. The aim of this review is to summarize the findings on the role of TIP60 as a coregulator for different classes of NRs and its overall functional implications. We also discuss the latest studies linking TIP60 to NR-associated metabolic disorders and cancers for its potential use as a therapeutic drug target in future.

Nordihydroguaiaretic Acid, a Lignan from Larrea tridentata (Creosote Bush), Protects Against American Lifestyle-Induced Obesity Syndrome Diet-Induced Metabolic Dysfunction in Mice

To determine the effects of nordihydroguaiaretic acid (NDGA) on metabolic and molecular changes in response to feeding a typical American fast food or Western diet, mice were fed an American lifestyle-induced obesity syndrome (ALIOS) diet and subjected to metabolic analysis. Male C57BL/6J mice were randomly assigned to the ALIOS diet, the ALIOS diet supplemented with NDGA (NDGA+ALIOS), or a control diet and were maintained on the specific diet for 8 weeks. Mice fed the ALIOS diet showed increased body, liver, and epididymal fat pad weight as well as increased plasma alanine transaminase (ALT) and aspartate aminotransferase (AST) levels (a measure of liver injury) and liver triglyceride content. Coadministration of NDGA normalized body and epididymal fat pad weight, ALT and AST levels, and liver triglycerides. NDGA treatment also improved insulin sensitivity but not glucose intolerance in mice fed the ALIOS diet. In mice fed the NDGA+ALIOS diet, NDGA supplementation induced peroxisome proliferator-activated receptor α (PPARα; the master regulator of fatty acid oxidation) and mRNA levels of carnitine palmitoyltransferases Cpt1c and Cpt2, key genes involved in fatty acid oxidation, compared with the ALIOS diet. NDGA significantly reduced liver endoplasmic reticulum (ER) stress response C/EBP homologous protein, compared with chow or the ALIOS diet, and also ameliorated ALIOS diet-induced elevation of apoptosis signaling protein, caspase 3. Likewise, NDGA downregulated the ALIOS diet-induced mRNA levels of Pparg, fatty acid synthase Fasn, and diacylglycerol acyltransferase Dgat2 NDGA treatment of ALIOS-fed mice upregulated the hepatic expression of antioxidant enzymes, glutathione peroxidase 4, and peroxiredoxin 3 proteins. In conclusion, we provide evidence that NDGA improves metabolic dysregulation by simultaneously modulating the PPARα transcription factor and key genes involved in fatty acid oxidation, key antioxidant and lipogenic enzymes, and apoptosis and ER stress signaling pathways.

PPARα Is Necessary for Radiation-Induced Activation of Noncanonical TGFβ Signaling in the Heart

High-dose ionizing radiation is known to induce adverse effects such as inflammation and fibrosis in the heart. Transcriptional regulators PPARα and TGFβ are known to be involved in this radiation response. PPARα, an anti-inflammatory transcription factor controlling cardiac energy metabolism, is inactivated by irradiation. The pro-inflammatory and pro-fibrotic TGFβ is activated by irradiation via SMAD-dependent and SMAD-independent pathways. The goal of this study was to investigate how altering the level of PPARα influences the radiation response of these signaling pathways. For this purpose, we used genetically modified C57Bl/6 mice with wild type (+/+), heterozygous (+/-) or homozygous (-/-) PPARα genotype. Mice were locally irradiated to the heart using doses of 8 or 16 Gy; the controls were sham-irradiated. The heart tissue was investigated using label-free proteomics 20 weeks after the irradiation and the predicted pathways were validated using immunoblotting, ELISA, and immunohistochemistry. The heterozygous PPARα mice showed most radiation-induced changes in the cardiac proteome, whereas the homozygous PPARα mice showed the least changes. Irradiation induced SMAD-dependent TGFβ signaling independently of the PPARα status, but the presence of PPARα was necessary for the activation of the SMAD-independent pathway. These data indicate a central role of PPARα in cardiac response to ionizing radiation.

Stereochemical and structural effects of (2R,6R)-hydroxynorketamine on the mitochondrial metabolome in PC-12 cells

BACKGROUND

Impairment in mitochondrial biogenesis and function plays a key role in depression and anxiety, both of which being associated with changes in fatty acid and phospholipid metabolism. The antidepressant effects of (R,S)-ketamine have been linked to its conversion into (2S,6S;2R,6R)-hydroxynorketamine (HNK); however, the connection between structure and stereochemistry of ketamine and HNK in the mitochondrial homeostatic response has not yet been fully elucidated at a metabolic level.

METHODS

We used a multi-platform, non-targeted metabolomics approach to study the change in mitochondrial metabolome of PC-12 cells treated with ketamine and HNK enantiomers. The identified metabolites were grouped into pathways in order to assess global responses.

RESULTS

Treatment with (2R,6R)-HNK elicited the significant change in 49 metabolites and associated pathways implicated in fundamental mitochondrial functions such as TCA cycle, branched-chain amino acid biosynthetic pathway, glycoxylate metabolic pathway, and fatty acid β-oxidation. The affected metabolites included glycerate, citrate, leucine, N,N-dimethylglycine, 3-hexenedioic acid, and carnitine and attenuated signals associated with 9 fatty acids and elaidic acid. Important metabolites involved in the purine and pyrimidine pathways were also affected by (2R-6R)-HNK. This global metabolic profile was not as strongly impacted by treatment with (2S,6S)-HNK, (R)- and (S)-ketamine and in some instances opposite effects were observed.

CONCLUSIONS

The present data provide an overall view of the metabolic changes in mitochondrial function produced by (2R,6R)-HNK and related ketamine compounds and offer an insight into the source of the observed variance in antidepressant response elicited by the compounds.

The role of the lipidome in obesity-mediated colon cancer risk

Obesity is a state of chronic inflammation influenced by lipids such as fatty acids and their secondary oxygenated metabolites deemed oxylipids. Many such lipid mediators serve as potent signaling molecules of inflammation, which can further alter lipid metabolism and lead to carcinogenesis. For example, sphingosine-1-phosphate activates cyclooxygenase-2 in endothelial cells resulting in the conversion of arachidonic acid (AA) to prostaglandin E₂ (PGE₂). PGE₂ promotes colon cancer cell growth. In contrast, the less studied path of AA oxygenation via cytochrome p450 enzymes produces epoxyeicosatetraenoic acids (EETs), whose anti-inflammatory properties cause shrinking of enlarged adipocytes, a characteristic of obesity, through the liberation of fatty acids. It is now thought that EET depletion occurs in obesity and may contribute to colon cell carcinogenesis. Meanwhile, gangliosides, a type of sphingolipid, are cell surface signaling molecules that contribute to the apoptosis of colon tumor cells. Many of these discoveries have been made recently and the mechanisms are still not fully understood, leading to an exciting new chapter of lipidomic research. In this review, mechanisms behind obesity-associated colon cancer are discussed with a focus on the role of small lipid signaling molecules in the process. Specifically, changes in lipid metabolite levels during obesity and the development of colon cancer, as well as novel biomarkers and targets for therapy, are discussed.

Cholecystokinin is involved in triglyceride fatty acid uptake by rat adipose tissue

The incorporation of plasma triglyceride (TG) fatty acids to white adipose tissue (WAT) depends on lipoprotein lipase (LPL), which is regulated by angiopoietin-like protein-4 (ANGPTL-4), an unfolding molecular chaperone that converts active LPL dimers into inactive monomers. The production of ANGPTL-4 is promoted by fasting and repressed by feeding. We hypothesized that the postprandial hormone cholecystokinin (CCK) facilitates the storage of dietary TG fatty acids in WAT by regulating the activity of the LPL/ANGPTL-4 axis and that it does so by acting directly on CCK receptors in adipocytes. We report that administration of CCK-8 (a bioactive fragment of CCK) to rats: (i) reduces plasma ANGTPL-4 levels; (ii) represses Angptl-4 expression in WAT and (iii) simultaneously enhances LPL activity in this tissue without inducing Lpl expression. In vivo CCK-8 effects are specifically antagonized by the CCK-2 receptor (CCK-2R) antagonist, L-365,260. Moreover, CCK-8 downregulates Angptl-4 expression in wild-type pre-adipocytes, an effect that is not observed in engineered pre-adipocytes lacking CCK-2R. These effects have functional consequences as CCK-8 was found to promote the uptake of dietary fatty acids by WAT, as demonstrated by means of proton nuclear magnetic resonance (¹H-NMR). The efficacy of acute CCK-8 administration was not reduced after chronic CCK-8 treatment. Moreover, the effects of CCK-8 on WAT were not associated to the increase of circulating insulin. Our results show that cholecystokinin promotes lipid storage in WAT by acting on adipocyte CCK-2R, suggesting a pivotal role for CCK in TG homeostasis.

New thiazolidinedione LPSF/GQ-2 inhibits NFκB and MAPK activation in LPS-induced acute lung inflammation

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are responsible for high mortality rates in critical patients. Despite >50 years of intensive research, there is no pharmacologically effective treatment to treat ALI. PPARs agonists, chemically named thiazolidinediones (TZDs) have emerged as potential drugs for the treatment of ALI and ARDS due to their anti-inflammatory efficacy. The present study aims to evaluate the potential anti-inflammatory effects of new TZDs derivatives, LPSF/GQ-2 and LPSF/RA-4, on ALI induced by LPS. BALB/c mice were divided into five groups: 1) Control; 2) LPS intranasal 25 μg; 3) LPSF/GQ-2 30 mg/kg + LPS; 4) LPSF/RA-4 20 mg/kg + LPS; and 5) DEXA 1 mg/Kg + LPS. BALF analyses revealed that LPSF/GQ-2 and LPSF/RA-4 reduced NO levels in BALF and inflammatory cell infiltration induced by LPS. MPO levels were also reduced by the LPSF/GQ-2 and LPSF/RA-4 pre-treatments. In contrast, histopathological analyses showed better tissue protection with LPSF/GQ-2 than DEXA and LPSF/RA-4 groups. Similarly, LPSF/GQ-2 reduced inflammatory markers (IL-1, iNOS, TNFα, IL-1β, IL-6) better than LPSF/RA-4. The LPSF/GQ-2 anti-inflammatory action could be attributed to the inhibition of NFκB, ERK, p38, and PARP pathways. In contrast, LPSF/RA-4 had no effect on the expression of p38, JNK, NFκB. The present study indicates that LPSF/GQ-2 presents a potential therapeutic role as an anti-inflammatory drug for ALI.

BAY 11-7085 induces glucocorticoid receptor activation and autophagy that collaborate with apoptosis to induce human synovial fibroblast cell death

Inhibition of proapoptotic pathways in synovial fibroblasts is one of the major causes of synovial proliferation and hyperplasia in rheumatic diseases. We have shown previously that NF-κB inhibitor BAY 11-7085, through inactivation of PPAR-γ, induces apoptosis in human synovial fibroblasts. In this work we showed that BAY 11-7085 induced autophagy that preceded BAY 11-7085-induced apoptosis. Of interest, BAY 11-7085 induced Serine 211 phosphorylation and degradation of glucocorticoid receptor (GR). Glucocorticoid prednisolone induced both activation and degradation of GR, as well as autophagy in synovial fibroblasts. BAY 11-7085-induced cell death was significantly decreased with glucocorticoid inhibitor mifepristone and with inhibitors of autophagy. Both BAY 11-7085-induced autophagy and GR activation were down regulated with PPAR-γ agonist, 15d-PGJ2 and MEK/ERK inhibitor UO126. Inhibition of autophagy markedly decreased endogenous and BAY 11-7085-induced ERK phosphorylation, suggesting a positive feed back loop between ERK activation and autophagy in synovial fibroblasts. Co-transfection of MEK1 with PPAR-γ1 in HEK293 cells caused known inhibitory phosphorylation of PPAR-γ1 (Serine 112) and enhanced GR degradation, in the absence or presence of prednisolone. Furthermore, GR was both phosphorylated on Serine 211 and down regulated in synovial fibroblasts during serum starvation induced autophagy. These results showed that GR activation and PPAR-γ inactivation mediated BAY 11-7085-induced autophagy.

Heme oxygenase-1 induction by rosiglitazone via PKCα/AMPKα/p38 MAPKα/SIRT1/PPARγ pathway suppresses lipopolysaccharide-mediated pulmonary inflammation

HO-1 (heme oxygenase-1), an antioxidant enzyme, induced by rosiglitazone (PPAR ligands) can be a potential treatment of inflammation. However, the mechanisms of rosiglitazone-induced HO-1 expression in human pulmonary alveolar epithelial cells (HPAEpiCs) remain largely unknown. In this study, we found that upregulation of HO-1 in vitro or in vivo by rosiglitazone attenuated VCAM-1 gene expression and monocyte adhesion to HPAEpiCs challenged with lipopolysaccharide (LPS). The inhibitory effects of rosiglitazone on LPS-mediated responses were reversed by transfection with HO-1 siRNA. LPS-induced VCAM-1 expression was mediated through NF-κB activation which was attenuated by rosiglitazone via suppressing p65 activation and translocation into the nucleus. Moreover, pretreatment with the inhibitor of PKCs (H7), PKCα (Gö6976), AMPKα (Compound C), p38 MAPKα (p38i VIII), SIRT1 (Sirtinol), or PPARγ (T0070907) and transfection with siRNA of PKCα, AMPKα, p38 MAPKα, SIRT1, or PPARγ abolished the rosiglitazone-induced HO-1 expression in HPAEpiCs. Further studies indicated that rosiglitazone stimulated SIRT1 deacetylase leading to PGC1α translocation from the cytosol into the nucleus, promoting fragmentation of NCoR and phosphorylation of PPARγ. Subsequently, PPARγ was activated by phosphorylation of PKCα, AMPKα, p38 MAPKα, and SIRT1, which turned on transcription of HO-1 gene by binding to PPAR response element (PPRE) and enhancing PPARγ promoter activity. These results suggested that rosiglitazone-induced HO-1 expression is mediated through PKCα/AMPKα/p38 MAPKα/SIRT1-dependent deacetylation of Ac-PGC1α and fragmentation of NCoR/PPARγ activation in HPAEpiCs. Up-regulation of HO-1 protected against the inflammatory responses triggered by LPS, at least in part, through attenuation of NF-κB.

Cardioprotective Regimen of Adaptation to Chronic Hypoxia Diversely Alters Myocardial Gene Expression in SHR and SHR-mtBN Conplastic Rat Strains

Adaptation to continuous normobaric hypoxia (CNH) protects the heart against acute ischemia/reperfusion injury. Recently, we have demonstrated the infarct size-limiting effect of CNH also in hearts of spontaneously hypertensive rats (SHR) and in conplastic SHR-mt^BN strain characterized by the selective replacement of the mitochondrial genome of SHR with that of more ischemia-resistant Brown Norway rats. Importantly, cardioprotective effect of CNH was more pronounced in SHR-mt^BN than in SHR. Thus, here we aimed to identify candidate genes which may contribute to this difference between the strains. Rats were adapted to CNH (FiO₂ 0.1) for 3 weeks or kept at room air as normoxic controls. Screening of 45 transcripts was performed in left ventricles using Biomark Chip. Significant differences between the groups were analyzed by univariate analysis (ANOVA) and the genes contributing to the differences between the strains unmasked by CNH were identified by multivariate analyses (PCA, SOM). ANOVA with Bonferroni correction revealed that transcripts differently affected by CNH in SHR and SHR-mt^BN belong predominantly to lipid metabolism and antioxidant defense. PCA divided four experimental groups into two main clusters corresponding to chronically hypoxic and normoxic groups, and differences between the strains were more pronounced after CNH. Subsequently, the following 14 candidate transcripts were selected by PCA, and confirmed by SOM analyses, that can contribute to the strain differences in cardioprotective phenotype afforded by CNH: Alkaline ceramidase 2 (Acer2), Fatty acid translocase (Cd36), Aconitase 1 (Aco1), Peroxisome proliferator activated receptor gamma (Pparg), Hemoxygenase 2 (Hmox2), Phospholipase A2 group IIA (Ppla2g2a), Dynamin-related protein (Drp), Protein kinase C epsilon (Pkce), Hexokinase 2 (Hk2), Sphingomyelin synthase 2 (Sgms2), Caspase 3 (Casp3), Mitofussin 1 (Mfn1), Phospholipase A2 group V (Pla2g5), and Catalase (Cat). Our data suggest that the stronger cardioprotective phenotype of conplastic SHR-mt^BN strain afforded by CNH is associated with either preventing the drop or increasing the expression of transcripts related to energy metabolism, antioxidant response and mitochondrial dynamics.

CDK5 promotes renal tubulointerstitial fibrosis in diabetic nephropathy via ERK1/2/PPARγ pathway

Cyclin-dependent kinase 5 (CDK5) has been documented in podocyte injuries in diabetic nephropathy (DN), however its role in renal tubular epithelial cells has not been elucidated. We report here that CDK5 is detrimental and promotes tubulointerstitial fibrosis (TIF) via the extracellular signal-regulated kinase 1/2 (ERK1/2)/peroxisome proliferator-activated receptor gamma (PPRAγ) pathway in DN. In high glucose cultured NRK52E cells, blocking CDK5 activity inhibited epithelial-to-mesenchymal transition (EMT) and fibrosis via ERK1/2/PPARγ pathway. In diabetic rats, CDK5 inhibitor roscovitine decreased renal fibrosis and improved renal function as demonstrated by a decrease in levels of blood urine nitrogen (BUN), serum creatinine and β2-microglobulin. Further studies revealed that improved renal fibrosis and function in diabetic rats were associated with inactivation of ERK1/2 and PPARγ signaling pathways. In late staged DN patients, the upregulation of CDK5 and p35 activated phosphorylated ERK1/2 and PPARγ, leading to decreased levels of E-cadherin but increased Vimentin and Collagen IV. Accordingly, renal fibrosis and function were worsened as revealed by decreased estimated glomerular filtration rate (eGFR) and increased serum BUN, creatinine, β2-microglobulin, 24-hour proteinuria and urine albumin to creatinine ratio (UACR). These findings demonstrate a novel mechanism that CDK5 increases tubulointerstitial fibrosis by activating the ERK1/2/PPARγ pathway and EMT in DN. CDK5 might have therapeutic potential in diabetic nephropathy.

Olfactory receptor 544 reduces adiposity by steering fuel preference toward fats

Olfactory receptors (ORs) are present in tissues outside the olfactory system; however, the function of these receptors remains relatively unknown. Here, we determined that olfactory receptor 544 (Olfr544) is highly expressed in the liver and adipose tissue of mice and regulates cellular energy metabolism and obesity. Azelaic acid (AzA), an Olfr544 ligand, specifically induced PKA-dependent lipolysis in adipocytes and promoted fatty acid oxidation (FAO) and ketogenesis in liver, thus shifting the fuel preference to fats. After 6 weeks of administration, mice fed a high-fat diet (HFD) exhibited a marked reduction in adiposity. AzA treatment induced expression of PPAR-α and genes required for FAO in the liver and induced the expression of PPAR-γ coactivator 1-α (Ppargc1a) and uncoupling protein-1 (Ucp1) genes in brown adipose tissue (BAT). Moreover, treatment with AzA increased insulin sensitivity and ketone body levels. This led to a reduction in the respiratory quotient and an increase in the FAO rate, as indicated by indirect calorimetry. AzA treatment had similar antiobesogenic effects in HFD-fed ob/ob mice. Importantly, AzA-associated metabolic changes were completely abrogated in HFD-fed Olfr544-/- mice. To our knowledge, this is the first report to show that Olfr544 orchestrates the metabolic interplay between the liver and adipose tissue, mobilizing stored fats from adipose tissue and shifting the fuel preference to fats in the liver and BAT.

In Vivo Effects of Lipopolysaccharide on Peroxisome Proliferator-Activated Receptor Expression in Juvenile Gilthead Seabream (Sparus Aurata)

Fish are constantly exposed to microorganisms in the aquatic environment, many of which are bacterial pathogens. Bacterial pathogens activate the innate immune response in fish involving the production of pro-inflammatory molecules that, in addition to their immune-related role, can affect non-immune tissues. In the present study, we aimed at investigating how inflammatory responses can affect metabolic homeostasis in the gilthead seabream (Sparus aurata), a teleost of considerable economic importance in Southern European countries. Specifically, we mimicked a bacterial infection by in vivo administration of lipopolysaccharide (LPS, 6 mg/kg body weight) and measured metabolic parameters in the blood and, importantly, the mRNA expression levels of the three isotypes of peroxisome proliferator activated receptors (PPARα, β, and γ) in metabolically-relevant tissues in seabream. PPARs are nuclear receptors that are important for lipid and carbohydrate metabolism in mammals and that act as biological sensors of altered lipid metabolism. We show here that LPS-induced inflammatory responses result in the modulation of triglyceride plasma levels that are accompanied most notably by a decrease in the hepatic mRNA expression levels of PPARα, β, and γ and by the up-regulation of PPARγ expression only in adipose tissue and the anterior intestine. In addition, LPS-induced inflammation results in an increase in the hepatic mRNA expression and protein activity levels of members of the mitogen-activated protein kinase (MAPK) family, known in mammals to regulate the transcription and activity of PPARs. Our results provide evidence for the involvement of PPARs in the metabolic response to inflammatory stimuli in seabream and offer insights into the molecular mechanisms underlying the redirection of metabolic activities under inflammatory conditions in vertebrates.

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.

Re-adaption on Earth after Spaceflights Affects the Mouse Liver Proteome

Harsh environmental conditions including microgravity and radiation during prolonged spaceflights are known to alter hepatic metabolism. Our studies have focused on the analysis of possible changes in metabolic pathways in the livers of mice from spaceflight project "Bion-M 1". Mice experienced 30 days of spaceflight with and without an additional re-adaption period of seven days compared to control mice on Earth. To investigate mice livers we have performed proteomic profiling utilizing shotgun mass spectrometry followed by label-free quantification. Proteomic data analysis provided 12,206 unique peptides and 1,086 identified proteins. Label-free quantification using MaxQuant software followed by multiple sample statistical testing (ANOVA) revealed 218 up-regulated and 224 down-regulated proteins in the post-flight compared to the other groups. Proteins related to amino acid metabolism showed higher levels after re-adaption, which may indicate higher rates of gluconeogenesis. Members of the peroxisome proliferator-activated receptor pathway reconstitute their level after seven days based on a decreased level in comparison with the flight group, which indicates diminished liver lipotoxicity. Moreover, bile acid secretion may regenerate on Earth due to reconstitution of related transmembrane proteins and CYP superfamily proteins elevated levels seven days after the spaceflight. Thus, our study demonstrates reconstitution of pharmacological response and decreased liver lipotoxicity within seven days, whereas glucose uptake should be monitored due to alterations in gluconeogenesis.

Conjugated Linoleic Acid Supplementation Improves Maternal High Fat Diet-Induced Programming of Metabolic Dysfunction in Adult Male Rat Offspring

The developmental origins of health and disease hypothesis proposes that an adverse early life environment, including in utero exposure to a maternal obesogenic environment, can lead to an increased long-term risk of obesity and related metabolic complications in offspring. We assessed whether maternal supplementation with conjugated linoleic acid (CLA) could prevent some of these adverse effects in offspring exposed to a maternal high fat diet. Sprague-Dawley dams consumed either a: control (CD), control with CLA (CLA), high fat (HF) or high fat with CLA (HFCLA) diet 10 days prior to mating and throughout pregnancy/lactation. Male offspring were weaned onto a standard chow diet. Body composition was quantified by DXA and oral glucose tolerance tests conducted on adult offspring. Gene/protein expression and histological analysis were conducted in adipose tissue. Offspring from HF dams had increased body weight, body fat deposition, impaired insulin sensitivity and adipocyte hypertrophy; all of which were rescued in HFCLA offspring. Molecular and histological analyses of the adipose tissue suggest that disturbances in adipogenesis may mediate the metabolic dysfunction observed in HF offspring. Therefore, CLA supplementation to a maternal obesogenic diet may be a promising strategy to prevent adverse programming outcomes.

The potential of natural products for targeting PPARα

Peroxisome proliferator activated receptors (PPARs) α, -γ and -β/δ are ligand-activated transcription factors and members of the superfamily of nuclear hormone receptor. These receptors play key roles in maintaining glucose and lipid homeostasis by modulating gene expression. PPARs constitute a recognized druggable target and indeed several classes of drugs used in the treatment of metabolic disease symptoms, such as dyslipidemia (fibrates, e.g. fenofibrate and gemfibrozil) and diabetes (thiazolidinediones, e.g. rosiglitazone and pioglitazone) are ligands for the various PPAR isoforms. More precisely, antidiabetic thiazolidinediones act on PPARγ, while PPARα is the main molecular target of antidyslipidemic fibrates. Over the past few years, our understanding of the mechanism underlying the PPAR modulation of gene expression has greatly increased. This review presents a survey on terrestrial and marine natural products modulating the PPARα system with the objective of highlighting how the incredible chemodiversity of natural products can provide innovative leads for this "hot" target.

Docosahexaenoic acid promotes oligodendrocyte differentiation via PPAR-γ signalling and prevents tumor necrosis factor-α-dependent maturational arrest

Docosahexaenoic acid (DHA) is an essential omega-3 fatty acid known to be neuroprotective in several models of human diseases, including multiple sclerosis. The protective effects of DHA are largely attributed to its ability to interfere with the activity of transcription factors controlling immune and inflammatory responses, including the agonist-dependent transcription factor peroxisome proliferator-activated receptor-γ (PPAR-γ). In this study, we used primary oligodendrocyte progenitor (OP) cultures from neonatal rat brain to investigate whether DHA could influence OP maturation and directly promote myelination, as previously reported for selective PPAR-γ agonists. We show that, similarly to the selective PPAR-γ agonist pioglitazone (PGZ), DHA promotes OP maturation and counteracts the maturational arrest induced by TNF-α, used to mimic inflammatory conditions. The PPAR-γ antagonist GW9662 prevented both DHA-induced OP maturation and PPAR-γ nuclear translocation, supporting the hypothesis that DHA acts through the activation of PPAR-γ. In addition, both PGZ and DHA induced the phosphorylation of extracellular signal-regulated-kinase 1-2 (ERK1/2), in a PPAR-γ-dependent manner. ERK1/2 activity is known to regulate the transition from OPs to immature oligodendrocytes and the presence of specific inhibitors of ERK1/2 phosphorylation (U0126 or PD98059) prevented the differentiating effects of both DHA and PGZ. These results indicate that DHA might influence the process of OP maturation through its PPAR-γ agonistic activity and provide novel molecular mechanisms for the action of this dietary fatty acid, further supporting the nutritional intervention in demyelinating diseases such as multiple sclerosis.

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.

Commensal gut bacteria modulate phosphorylation-dependent PPARγ transcriptional activity in human intestinal epithelial cells

In healthy subjects, the intestinal microbiota interacts with the host’s epithelium, regulating gene expression to the benefit of both, host and microbiota. The underlying mechanisms remain poorly understood, however. Although many gut bacteria are not yet cultured, constantly growing culture collections have been established. We selected 57 representative commensal bacterial strains to study bacteria-host interactions, focusing on PPARγ, a key nuclear receptor in colonocytes linking metabolism and inflammation to the microbiota. Conditioned media (CM) were harvested from anaerobic cultures and assessed for their ability to modulate PPARγ using a reporter cell line. Activation of PPARγ transcriptional activity was linked to the presence of butyrate and propionate, two of the main metabolites of intestinal bacteria. Interestingly, some stimulatory CMs were devoid of these metabolites. A Prevotella and an Atopobium strain were chosen for further study, and shown to up-regulate two PPARγ-target genes, ANGPTL4 and ADRP. The molecular mechanisms of these activations involved the phosphorylation of PPARγ through ERK1/2. The responsible metabolites were shown to be heat sensitive but markedly diverged in size, emphasizing the diversity of bioactive compounds found in the intestine. Here we describe different mechanisms by which single intestinal bacteria can directly impact their host’s health through transcriptional regulation.

PPARs in the central nervous system: roles in neurodegeneration and neuroinflammation

Over 25 years have passed since peroxisome proliferators-activated receptors (PPARs), were first described. Like other members of the nuclear receptors superfamily, PPARs have been defined as critical sensors and master regulators of cellular metabolism. Recognized as ligand-activated transcription factors, they are involved in lipid, glucose and amino acid metabolism, taking part in different cellular processes, including cellular differentiation and apoptosis, inflammatory modulation and attenuation of acute and chronic neurological damage in vivo and in vitro. Interestingly, PPAR activation can simultaneously reprogram the immune response, stimulate metabolic and mitochondrial functions, promote axonal growth, induce progenitor cells to differentiate into myelinating oligodendrocytes, and improve brain clearance of toxic molecules such as β-amyloid peptide. Although the molecular mechanisms and cross-talk with different molecular pathways are still the focus of intense research, PPARs are considered potential therapeutic targets for several neuropathological conditions, including degenerative disorders such as Alzheimer's, Parkinson's and Huntington's disease. This review considers recent advances regarding PPARs, as well as new PPAR agonists. We focus on the mechanisms behind the neuroprotective effects exerted by PPARs and summarise the roles of PPARs in different pathologies of the central nervous system, especially those associated with degenerative and inflammatory mechanisms.

Antihypertensive effects of peroxisome proliferator-activated receptor-β/δ activation

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily of ligand-activated transcription factors, which is composed of three members encoded by distinct genes: PPARα, PPARβ/δ, and PPARγ. The biological actions of PPARα and PPARγ and their potential as a cardiovascular therapeutic target have been extensively reviewed, whereas the biological actions of PPARβ/δ and its effectiveness as a therapeutic target in the treatment of hypertension remain less investigated. Preclinical studies suggest that pharmacological PPARβ/δ activation induces antihypertensive effects in direct [spontaneously hypertensive rat (SHR), ANG II, and DOCA-salt] and indirect (dyslipemic and gestational) models of hypertension, associated with end-organ damage protection. This review summarizes mechanistic insights into the antihypertensive effects of PPARβ/δ activators, including molecular and functional mechanisms. Pharmacological PPARβ/δ activation induces genomic actions including the increase of regulators of G protein-coupled signaling (RGS), acute nongenomic vasodilator effects, as well as the ability to improve the endothelial dysfunction, reduce vascular inflammation, vasoconstrictor responses, and sympathetic outflow from central nervous system. Evidence from clinical trials is also examined. These preclinical and clinical outcomes of PPARβ/δ ligands may provide a basis for the development of therapies in combating hypertension.

Gender-Specific Mechanisms Underlying the Amelioration of High-Fat Diet-Induced Glucose Intolerance in B-Cell-Activating Factor Deficient Mice

It has recently been found that B cell activating factor (BAFF) plays an important role in the regulation of energy homeostasis. We also have previously reported that BAFF deficiency reverses high-fat (HF) diet-induced glucose intolerance by potentiating adipose tissue function. In the present study, we found that BAFF deficient (BAFF^-/-) mice exhibit gender-specific differences in protection against diet-induced glucose intolerance, and aimed to characterize the gender-dependent molecular alterations in energy metabolism. Under HF feeding conditions, serum BAFF level of female wild-type (WT) mice was considerably higher than that of male mice. Despite increased body weight gain, both male and female BAFF^-/- mice showed significantly improved glucose tolerance compared to their WT counterparts. Expressions of genes involved in glucose transport, thermogenesis and lipid oxidation were up-regulated in brown adipose tissues of both male and female BAFF^-/- mice. Interestingly, the expression of thermogenic genes in subcutaneous adipose tissue was significantly enhanced in female BAFF^-/- compared to WT mice, but the difference was not observed between male BAFF^-/- and WT mice. The enhanced thermogenic program was confirmed by higher protein levels of UCP1 and irisin in female BAFF^-/- than in WT mice. Additionally, adiponectin production in white adipose tissues and AMPK phosphorylation in subcutaneous adipose tissue were also significantly elevated in female BAFF^-/- compared to WT mice, but not in male BAFF^-/- mice. Our findings define a comprehensive scenario for the enhancing effect of BAFF depletion on glucose tolerance wherein the underlying mechanism is, at least in part, gender-specific, and suggest that gender difference should be considered as an important factor in the use of BAFF blockade as a therapeutic approach for the prevention and treatment of type 2 diabetes.

Hepatic aberrant glycosylation by N-acetylglucosaminyltransferase V accelerates HDL assembly

Glycosylation is involved in various pathophysiological conditions. N-Acetylglucosaminyltransferase V (GnT-V), catalyzing β1-6 branching in asparagine-linked oligosaccharides, is one of the most important glycosyltransferases involved in cancer and the immune system. Recent findings indicate that aberrant N-glycan structure can modify lipid metabolism. In this study, we investigated the effects of aberrant glycosylation by GnT-V on high-density lipoprotein cholesterol (HDL) assembly. We used GnT-V transgenic (Tg) mice and GnT-V Hep3B cell (human hepatoma cell line) transfectants. The study also included 96 patients who underwent medical health check-ups. Total serum cholesterol levels, particularly HDL-cholesterol (HDL-C) levels, were significantly increased in Tg vs. wild-type (WT) mice. Hepatic expression of apolipoprotein AI (ApoAI) and ATP-binding cassette subfamily A member 1 (ABCA1), two important factors in HDL assembly, were higher in Tg mice compared with WT mice. ApoAI and ABCA1 were also significantly elevated in GnT-V transfectants compared with mock-transfected cells. Moreover, ApoAI protein in the cultured media of GnT-V transfectants was significantly increased. Finally, we found a strong correlation between serum GnT-V activity and HDL-C concentration in human subjects. Multivariate logistic analyses demonstrated that GnT-V activity was an independent and significant determinant for serum HDL-C levels even adjusted with age and gender differences. Further analyses represented that serum GnT-V activity had strong correlation especially with the large-size HDL particle concentration. These findings indicate that enhanced hepatic GnT-V activity accelerated HDL assembly and could be a novel mechanism for HDL synthesis.

A grape seed procyanidin extract inhibits HDAC activity leading to increased Pparα phosphorylation and target-gene expression

SCOPE

Histone deacetylases (HDACs) have emerged as epigenetic regulators of risk factors associated with the metabolic syndrome (MetS), and certain botanical extracts have proven to be potent HDAC inhibitors. Understanding the role of dietary procyanidins in HDAC inhibition is important in exploring the therapeutic potential of natural products.

METHODS

C57BL/6 mice were gavaged with vehicle (water) or grape seed procyanidin extract (GSPE, 250 mg/kg) and terminated 14 h later. Liver and serum were harvested to assess the effect of GSPE on HDAC activity, histone acetylation, Pparα activity and target-gene expression, and serum lipid levels.

RESULTS

GSPE increased histone acetylation and decreased Class I HDAC activity in vivo, and dose-dependently inhibited recombinant HDAC2 and 3 activities in vitro. Accordingly, Pparα gene and phosphorylated protein expression were increased, as were target genes involved in fatty acid catabolism, suggesting increased Pparα activity. Serum fibroblast growth factor 21 (Fgf21) was elevated, and triglyceride levels were reduced by 28%.

CONCLUSION

GSPE regulates HDAC and Pparα activities to modulate lipid catabolism and reduce serum triglycerides in vivo.

Biliverdin Reductase A Attenuates Hepatic Steatosis by Inhibition of Glycogen Synthase Kinase (GSK) 3β Phosphorylation of Serine 73 of Peroxisome Proliferator-activated Receptor (PPAR) α

Non-alcoholic fatty liver disease is the most rapidly growing form of liver disease and if left untreated can result in non-alcoholic steatohepatitis, ultimately resulting in liver cirrhosis and failure. Biliverdin reductase A (BVRA) is a multifunctioning protein primarily responsible for the reduction of biliverdin to bilirubin. Also, BVRA functions as a kinase and transcription factor, regulating several cellular functions. We report here that liver BVRA protects against hepatic steatosis by inhibiting glycogen synthase kinase 3β (GSK3β) by enhancing serine 9 phosphorylation, which inhibits its activity. We show that GSK3β phosphorylates serine 73 (Ser(P)⁷³) of the peroxisome proliferator-activated receptor α (PPARα), which in turn increased ubiquitination and protein turnover, as well as decreased activity. Interestingly, liver-specific BVRA KO mice had increased GSK3β activity and Ser(P)⁷³ of PPARα, which resulted in decreased PPARα protein and activity. Furthermore, the liver-specific BVRA KO mice exhibited increased plasma glucose and insulin levels and decreased glycogen storage, which may be due to the manifestation of hepatic steatosis observed in the mice. These findings reveal a novel BVRA-GSKβ-PPARα axis that regulates hepatic lipid metabolism and may provide unique targets for the treatment of non-alcoholic fatty liver disease.

Pioglitazone induces cell growth arrest and activates mitochondrial apoptosis in human uterine leiomyosarcoma cells by a peroxisome proliferator-activated receptor γ-independent mechanism

The peroxisome proliferator-activated receptor γ (PPARγ) agonists, thiazolidinediones, including pioglitazone (PIO) exhibit anti-tumour activities in cancer cells. The present study investigates the effects of PIO on cell proliferation and apoptosis in SK-UT-1 cells, a human uterine leiomyosarcoma cell line, and human uterine smooth muscle cells (HUtSMC). The proliferation and viability of SK-UT-1 cells treated with vehicle or PIO were assessed by cell counting and WST-1 assay. The activity of MEK/ERK and p38 MAPK signalling pathways and the expression of p53, the cyclin-dependent kinase inhibitor, p21, Bax, Bad and Bim proteins and cleaved caspase-3 were analysed by Western blotting. Quiescent SK-UT-1 cells intensively proliferate and display high levels of phosphorylated, activated MEK1/2, ERK1/2 and p38 MAPK. PIO (10 or 25 μM) induced time- and dose-dependently cell-growth arrest, reduced the cell numbers and effectively suppressed the over-activated MEK/ERK and p38 MAPK signalling pathways as evidenced by the abolished levels of phosphorylated MEK1/2, ERK1/2 and p38 MAPK. PIO activated the intrinsic apoptotic pathway, i.e. up-regulated the p53, p21, Bax and Bad proteins and cleaved caspase-3. PIO also reduced cell numbers of highly proliferative SK-UT-1 cells cultured in growth medium. The anti-proliferative and pro-apoptotic actions of PIO were not PPARγ dependent and exclusive for SK-UT-1 cells as PIO did not interfere with the proliferation of HUtSMC. The pronounced anti-tumorigenic effects of PIO in SK-UT-1 cells address an important issue about the relevance of the PPARγ agonist in the treatment of the human uterine leiomyosarcoma.

Stimulating effect of normal-dosing of fibrates on cell proliferation: word of warning

BACKGROUND

Fibrates are widely used hypolipidemic drugs, which serve as ligand of peroxisome proliferator-activated receptor α (PPARα). Recently, they have also been considered as potential anticancer agents. We studied effect of fibrates treatment on cell proliferation, expression of CYP2J2 and concomitant changes in expression of cell cycle regulatory proteins in three different human cell lines: HEK293, HepG2, and HT-29.

METHODS

We used WST-1 viability test, western blot and immunocytochemistry for detection of proteins of interests and analysis of cell cycle.

RESULTS

Our results showed that at lower concentrations of all tested fibrates, viability of all tested cell lines is increased, whereas at higher concentrations, repression is apparent. Unfortunately, the viability of tested cells is predominantly increased in a range of concentration which is reached in patient plasma. This phenomenon is accompanyed by elevation of CYP2J2, increased number of cyclin E-positive cells and decreased number of Cdc25A-positive cells in all tested cell lines, and elevated cyclin A expression in HepG2 and HT-29. These changes are concentration-dependent. We suppose that increased level of CYP2J2 could explain enhanced cell proliferation in lower concentration of fibrates.

CONCLUSION

Based on our results, we suggested there is no anti-cancer effect of fibrates in tested carcinoma cell lines.

Mechanisms and metabolic regulation of PPARα activation in Nile tilapia (Oreochromis niloticus)

Although the key metabolic regulatory functions of mammalian peroxisome proliferator-activated receptor α (PPARα) have been thoroughly studied, the molecular mechanisms and metabolic regulation of PPARα activation in fish are less known. In the first part of the present study, Nile tilapia (Nt)PPARα was cloned and identified, and high mRNA expression levels were detected in the brain, liver, and heart. NtPPARα was activated by an agonist (fenofibrate) and by fasting and was verified in primary hepatocytes and living fish by decreased phosphorylation of NtPPARα and/or increased NtPPARα mRNA and protein expression. In the second part of the present work, fenofibrate was fed to fish or fish were fasted for 4weeks to investigate the metabolic regulatory effects of NtPPARα. A transcriptomic study was also performed. The results indicated that fenofibrate decreased hepatic triglyceride and 18C-series fatty acid contents but increased the catabolic rate of intraperitoneally injected [1-(14)C] palmitate in vivo, hepatic mitochondrial β-oxidation efficiency, the quantity of cytochrome b DNA, and carnitine palmitoyltransferase-1a mRNA expression. Fenofibrate also increased serum glucose, insulin, and lactate concentrations. Fasting had stronger hypolipidemic and gene regulatory effects than those of fenofibrate. Taken together, we conclude that: 1) liver is one of the main target tissues of the metabolic regulation of NtPPARα activation; 2) dephosphorylation is the basal NtPPARα activation mechanism rather than enhanced mRNA and protein expression; 3) activated NtPPARα has a hypolipidemic effect by increasing activity and the number of hepatic mitochondria; and 4) PPARα activation affects carbohydrate metabolism by altering energy homeostasis among nutrients.