Three members of the human pyruvate dehydrogenase kinase gene family are direct targets of the peroxisome proliferator-activated receptor beta/delta

Single and Multiple Doses of Seladelpar Decrease Diurnal Markers of Bile Acid Synthesis in Mice

Peroxisome proliferator-activated receptors (PPARs) modulate bile metabolism and are important therapeutic options in cholestatic diseases. This study was aimed at understanding the effects of single and multiple doses of seladelpar, a PPARδ (peroxisome proliferator-activated receptor delta) agonist, on plasma C4 (a freely diffusible metabolite accepted as a proxy for de novo bile acid biosynthesis), Fibroblast Growth Factor 21 (Fgf21), and gene expression changes in the liver of male and female mice. C57BL/6 mice were treated with seladelpar 10 mg/kg/day or vehicle through oral gavage before lights out on Day 1 (single dose) or from Day 1 to Day 7 (multiple doses). Liver samples were obtained at 0, 1, 2, 4, 8, 12, 16, and 24 h postdosing, and plasma C4 and Fgf21 levels were measured. In vehicle-treated mice, C4 levels were higher in the dark cycle compared to the light cycle, with higher levels in females than in males. Plasma Fgf21 did not vary substantially over the dark-light cycle or show a sex-specific expression pattern. Seladelpar treatment significantly reduced plasma C4 and increased Fgf21 levels in both sexes, which coincided with a decrease in cholesterol 7α-hydroxylase mRNA and an increase in Fgf21 mRNA in the livers. Untargeted RNA sequencing revealed a strong correlation between the genes differentially expressed after single- and multiple-dose seladelpar treatment. PPAR-responsive genes, including pyruvate dehydrogenase kinase 4, acyl-CoA thioesterase 2, and angiopoietin-like 4, were upregulated. No changes in nuclear receptors, clock genes, and sex-specific genes were observed. Overall, these results are consistent with a model where seladelpar treatment reduces bile acid synthesis by upregulating Fgf21 and modulating other PPAR-responsive genes.

Novel Candidate Genes Detection Using Bayesian Network-Based Genome-Wide Association Study of Latent Traits in F2 Chicken Population

In chickens, economically important traits are commonly controlled by multiple genes and are often correlated. The genetic mechanisms underlying the correlated phenotypes likely involve pleiotropy or linkage disequilibrium, which is not handled properly in single-trait genome-wide association studies (GWAS). We employed factor analytical models to estimate the value of latent traits to reduce the dimensionality of the adjusted phenotypes. The dataset included phenotypes from 369 F2 chickens, categorised into six observable classes, namely body weight (BW), feed intake (FI), feed efficiency (FE), immunity (IMU), blood metabolites (BMB), and carcass (CC) traits. All birds were genotyped using a 60K SNP Beadchip. A Bayesian network (BN) algorithm was used to discern the recursive causal relationships among the inferred latent traits. Multi-Trait (MT) and Structural Equation Model (SEM) were applied for association analysis. Several candidate genes were detected across six phenotypic classes, namely the IPMK gene for BW and FI, and, the MTERF2 gene for BW and FE. The rs14565514 SNP, close to genes IPMK, UBE2D1, and CISD1, was recognised as a pleiotropic marker by both models. The NRG3 gene, located on chromosome 6, was associated with FI. CRISP2, RHAG, CYP2AC1, and CENPQ genes, located on chromosome 3, were detected for BMB through both MT- and SEM-GWAS. In general, the results indicated that the SEM-GWAS is superior to MT-GWAS due to considering the causal relationships among the traits, correcting the effects of the traits on each other, and also leading to the identification of pleiotropic SNP markers.

Eicosapentaenoic acid increases proportion of type 1 muscle fibers through PPARδ and AMPK pathways in rats

Muscle fiber type composition (% slow-twitch and % fast-twitch fibers) is associated with metabolism, with increased slow-twitch fibers alleviating metabolic disorders. Previously, we reported that dietary fish oil intake induced a muscle fiber-type transition in a slower direction in rats. The aim of this study was to determine the functionality of eicosapentaenoic acid (EPA), a unique fatty acid in fish oil, to skeletal muscle fiber type and metabolism in rats. Here, we showed that dietary EPA promotes whole-body oxidative metabolism and improves muscle function by increasing proportion of slow-twitch type 1 fibers in rats. Transcriptomic and metabolomic analyses revealed that EPA supplementation activated the peroxisome proliferator-activated receptor δ (PPARδ) and AMP-activated protein kinase (AMPK) pathways in L6 myotube cultures, which potentially increasing slow-twitch fiber share. This highlights the role of EPA as an exercise-mimetic dietary component that improves metabolism and muscle function, with potential benefits for health and athletic performance.

Dichloroacetate for Cancer Treatment: Some Facts and Many Doubts

Rarely has a chemical elicited as much controversy as dichloroacetate (DCA). DCA was initially considered a dangerous toxic industrial waste product, then a potential treatment for lactic acidosis. However, the main controversies started in 2008 when DCA was found to have anti-cancer effects on experimental animals. These publications showed contradictory results in vivo and in vitro such that a thorough consideration of this compound's in cancer is merited. Despite 50 years of experimentation, DCA's future in therapeutics is uncertain. Without adequate clinical trials and health authorities' approval, DCA has been introduced in off-label cancer treatments in alternative medicine clinics in Canada, Germany, and other European countries. The lack of well-planned clinical trials and its use by people without medical training has discouraged consideration by the scientific community. There are few thorough clinical studies of DCA, and many publications are individual case reports. Case reports of DCA's benefits against cancer have been increasing recently. Furthermore, it has been shown that DCA synergizes with conventional treatments and other repurposable drugs. Beyond the classic DCA target, pyruvate dehydrogenase kinase, new target molecules have also been recently discovered. These findings have renewed interest in DCA. This paper explores whether existing evidence justifies further research on DCA for cancer treatment and it explores the role DCA may play in it.

Molecular insights of a CBP/β-catenin-signaling inhibitor on nonalcoholic steatohepatitis-induced liver fibrosis and disorder

Nonalcoholic steatohepatitis (NASH) is a progressive fibrotic disease associated with an increased risk of developing hepatocellular carcinoma; at present, no efficient therapeutic strategy has been established. Herein, we examined the efficacy of PRI-724, a potent inhibitor of CBP/β-catenin signaling, for treating NASH-related liver fibrosis and disorder and characterized its mechanism. Choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD)-fed mice exhibited NASH-induced liver fibrosis that is characterized by steatosis, lobular inflammation, hepatocellular injury and collagen fibrils. To examine the therapeutic effect, CDAHFD-fed mice were administered PRI-724. Serum levels of ALT and pro-fibrotic molecule, i.e. Mac-2 bp, alpha smooth muscle actin, type I and type III collagens, decreased significantly. mRNA levels of the matrix metalloproteinases Mmp8 and Mmp9 in the liver were significantly increased, and increases in the abundance of MMP9-producing neutrophils and macrophages were observed. Marco+Mmp9+Cd68+ Kupffer cells were only observed in the livers of mice treated with PRI-724, and Mmp9 expression in Marco+Cd68+ Kupffer cells increased 4.3-fold. Moreover, hepatic expression of the lipid metabolism regulator, pyruvate dehydrogenase kinase 4 and liver lipid droplets also decreased significantly. PRI-724-treated NASH mice not only recovered from NASH-related liver fibrosis through the effect of PRI-724 down-regulating the expression of pro-fibrotic genes and up-regulating the expression of anti-fibrotic genes, but they also recovered from NASH-induced liver disorder. PRI-724, a selective CBP/β-catenin inhibitor, thus shows a potent therapeutic effect for NASH-related liver fibrosis and for decreasing adipose tissue in the liver.

Pharmacological activation of PPARβ/δ preserves mitochondrial respiratory function in ischemia/reperfusion via stimulation of fatty acid oxidation-linked respiration and PGC-1α/NRF-1 signaling

Myocardial ischemia/reperfusion (I/R) injury leads to significant impairment of cardiac function and remains the leading cause of morbidity and mortality worldwide. Activation of peroxisome proliferator-activated receptor β/δ (PPARβ/δ) confers cardioprotection via pleiotropic effects including antioxidant and anti-inflammatory actions; however, the underlying mechanisms are not yet fully elucidated. The aim of this study was to investigate the effect of PPARβ/δ activation on myocardial mitochondrial respiratory function and link this effect with cardioprotection after ischemia/reperfusion (I/R). For this purpose, rats were treated with the PPARβ/δ agonist GW0742 and/or antagonist GSK0660 in vivo. Mitochondrial respiration and ROS production rates were determined using high-resolution fluororespirometry. Activation of PPARβ/δ did not alter mitochondrial respiratory function in the healthy heart, however, inhibition of PPARβ/δ reduced fatty acid oxidation (FAO) and complex II-linked mitochondrial respiration and shifted the substrate dependence away from succinate-related energy production and towards NADH. Activation of PPARβ/δ reduced mitochondrial stress during in vitro anoxia/reoxygenation. Furthermore, it preserved FAO-dependent mitochondrial respiration and lowered ROS production at oxidative phosphorylation (OXPHOS)-dependent state during ex vivo I/R. PPARβ/δ activation was also followed by increased mRNA expression of components of FAO -linked respiration and of transcription factors governing mitochondrial homeostasis (carnitine palmitoyl transferase 1b and 2-CPT-1b and CPT-2, electron transfer flavoprotein dehydrogenase -ETFDH, peroxisome proliferator-activated receptor gamma co-activator 1 alpha- PGC-1α and nuclear respiratory factor 1-NRF-1). In conclusion, activation of PPARβ/δ stimulated both FAO-linked respiration and PGC-1α/NRF -1 signaling and preserved mitochondrial respiratory function during I/R. These effects are associated with reduced infarct size.

Regulation of Cardiac-Specific Proteins Expression by Moderate-Intensity Aerobic Exercise Training in Mice With Myocardial Infarction Induced Heart Failure Using MS-Based Proteomics

This study aims to systematically reveal the changes in protein levels induced by regular exercise in mice with ischemic-induced heart failure (HF). Aerobic exercise training for the ischemic-induced HF mice lasted for 4 weeks and then we used the liquid chromatography-mass spectrometry method to identify and quantify the protein profile in the myocardium of mice. As a whole, 1,304 proteins (597 proteins up-regulated; 707 proteins down-regulated) were differentially expressed between the exercise group and the sedentary group, including numerous proteins related to energy metabolism. The significant alteration of the component (E1 component subunit alpha and subunit beta) and the activity-regulating enzyme (pyruvate dehydrogenase kinase 2 and pyruvate dehydrogenase kinase 4) of pyruvate dehydrogenase complex and poly [ADP-ribose] polymerase 3, a nicotinamide adenine dinucleotide(+)-consuming enzymes, was further verified in targeted analysis. Generally, this proteomics profiling furnishes a systematic insight of the influence of aerobic exercise on HF.

PPARα, δ and FOXO1 Gene Silencing Overturns Palmitate-Induced Inhibition of Pyruvate Oxidation Differentially in C2C12 Myotubes

Simple Summary

Frequent high-dietary fat intake increases muscle lipid use and reduces muscle carbohydrate use, thereby inducing metabolic inflexibility. The latter term can be described as a poor muscle biochemical and molecular response to increased availability of insulin, which in the long term results in chronically excessive-high glucose levels in blood. Chronic hyperglycaemia is associated with many pathological conditions, including type 2 diabetes mellitus, which can cause severe health damages in humans. Here, we attempt to unravel the underlying mechanism and its associated factors behind the inhibition of muscle glucose use by a high-fat diet, thereby providing evidence for appropriate therapeutic intervention.

Abstract

The molecular mechanisms by which free fatty acids (FFA) inhibit muscle glucose oxidation is still elusive. We recently showed that C2C12 myotubes treated with palmitate (PAL) presented with greater protein expression levels of PDK4 and transcription factors PPARα and PPARδ and lower p-FOXO/t-FOXO protein ratios when compared to control. This was complemented with the hallmarks of metabolic inflexibility (MI), i.e., reduced rates of glucose uptake, PDC activity and maximal pyruvate-derived ATP production rates (MAPR). However, the relative contribution of these transcription factors to the increase in PDK4 and reduced glucose oxidation could not be established. Therefore, by using a similar myotube model, a series of individual siRNA gene silencing experiments, validated at transcriptional and translation levels, were performed in conjunction with measurements of glucose uptake, PDC activity, MAPR and concentrations of metabolites reflecting PDC flux (lactate and acetylcarnitine). Gene silencing of PPARα, δ and FOXO1 individually reduced PAL-mediated inhibition of PDC activity and increased glucose uptake, albeit by different mechanisms as only PPARδ and FOXO1 silencing markedly reduced PDK4 protein content. Additionally, PPARα and FOXO1 silencing, but not PPARδ, increased MAPR with PAL. PPARδ silencing also decreased FOXO1 protein. Since FOXO1 silencing did not alter PPARδ protein, this suggests that FOXO1 might be a PPARδ downstream target. In summary, this study suggests that the molecular mechanisms by which PAL reduces PDC-mediated glucose-derived pyruvate oxidation in muscle occur primarily through increased PPARδ and FOXO1 mediated increases in PDK4 protein expression and secondarily through PPARα mediated allosteric inhibition of PDC flux. Furthermore, since PPARδ seems to control FOXO1 expression, this may reflect an important role for PPARδ in preventing glucose oxidation under conditions of increased lipid availability.

PDK2: An Underappreciated Regulator of Liver Metabolism

Pyruvate metabolism is critical for all mammalian cells. The pyruvate dehydrogenase complex couples the pyruvate formed as the primary product of glycolysis to the formation of acetyl-CoA required as the primary substrate of the citric acid cycle. Dysregulation of this coupling contributes to alterations in metabolic flexibility in obesity, diabetes, cancer, and more. The pyruvate dehydrogenase kinase family of isozymes phosphorylate and inactive the pyruvate dehydrogenase complex in the mitochondria. This function makes them critical mediators of mitochondrial metabolism and drug targets in a number of disease states. The liver expresses multiple PDKs, predominantly PDK1 and PDK2 in the fed state and PDK1, PDK2, and PDK4 in the starved and diabetic states. PDK4 undergoes substantial transcriptional regulation in response to a diverse array of stimuli in most tissues. PDK2 has received less attention than PDK4 potentially due to the dramatic changes in transcriptional gene regulation. However, PDK2 is more responsive than the other PDKs to feedforward and feedback regulation by substrates and products of the pyruvate dehydrogenase complex. Although underappreciated, this makes PDK2 particularly important for the minute-to-minute fine control of the pyruvate dehydrogenase complex and a major contributor to metabolic flexibility. The purpose of this review is to characterize the underappreciated role of PDK2 in liver metabolism. We will focus on known biological actions and physiological roles as well as what roles PDK2 may play in disease states. We will also define current inhibitors and address their potential as therapeutic agents in the future.

Satellite glia as a critical component of diabetic neuropathy: Role of lipocalin-2 and pyruvate dehydrogenase kinase-2 axis in the dorsal root ganglion

Diabetic peripheral neuropathy (DPN) is a common complication of uncontrolled diabetes. The pathogenesis of DPN is associated with chronic inflammation in dorsal root ganglion (DRG), eventually causing structural and functional changes. Studies on DPN have primarily focused on neuronal component, and there is limited knowledge about the role of satellite glial cells (SGCs), although they completely enclose neuronal soma in DRG. Lipocalin-2 (LCN2) is a pro-inflammatory acute-phase protein found in high levels in diverse neuroinflammatory and metabolic disorders. In diabetic DRG, the expression of LCN2 was increased exclusively in the SGCs. This upregulation of LCN2 in SGCs correlated with increased inflammatory responses in DRG and sciatic nerve. Furthermore, diabetes-induced inflammation and morphological changes in DRG, as well as sciatic nerve, were attenuated in Lcn2 knockout (KO) mice. Lcn2 gene ablation also ameliorated neuropathy phenotype as determined by nerve conduction velocity and intraepidermal nerve fiber density. Mechanistically, studies using specific gene KO mice, adenovirus-mediated gene overexpression strategy, and primary cultures of DRG SGCs and neurons have demonstrated that LCN2 enhances the expression of mitochondrial gate-keeping regulator pyruvate dehydrogenase kinase-2 (PDK2) through PPARβ/δ, thereby inhibiting pyruvate dehydrogenase activity and increasing production of glycolytic end product lactic acid in DRG SGCs and neurons of diabetic mice. Collectively, our findings reveal a crucial role of glial LCN2-PPARβ/δ-PDK2-lactic acid axis in progression of DPN. Our results establish a link between pro-inflammatory LCN2 and glycolytic PDK2 in DRG SGCs and neurons and propose a novel glia-based mechanism and drug target for therapy of DPN. MAIN POINTS: Diabetes upregulates LCN2 in satellite glia, which in turn increases pyruvate dehydrogenase kinase-2 (PDK2) expression and lactic acid production in dorsal root ganglia (DRG). Glial LCN2-PDK2-lactic acid axis in DRG plays a crucial role in the pathogenesis of diabetic neuropathy.

Astrocytic pyruvate dehydrogenase kinase-2 is involved in hypothalamic inflammation in mouse models of diabetes

Hypothalamic inflammation plays an important role in disrupting feeding behavior and energy homeostasis as well as in the pathogenesis of obesity and diabetes. Here, we show that pyruvate dehydrogenase kinase (PDK)-2 plays a role in hypothalamic inflammation and its sequelae in mouse models of diabetes. Cell type-specific genetic ablation and pharmacological inhibition of PDK2 in hypothalamic astrocytes suggest that hypothalamic astrocytes are involved in the diabetic phenotype. We also show that the PDK2-lactic acid axis plays a regulatory role in the observed metabolic imbalance and hypothalamic inflammation in mouse primary astrocyte and organotypic cultures, through the AMPK signaling pathway and neuropeptidergic circuitry governing feeding behavior. Our findings reveal that PDK2 ablation or inhibition in mouse astrocytes attenuates diabetes-induced hypothalamic inflammation and subsequent alterations in feeding behavior.

Hypothalamic inflammation is involved in the pathogenesis of diabetes. The underlying mechanisms are unclear. Here, the authors show that astrocytic PDK2 ablation or inhibition attenuates hypothalamic inflammation in mouse models of diabetes.

[Full transcriptome analysis of gene expression in liver of mice in a comparative study of quercetin efficiency on two obesity models]

BACKGROUND

Quercetin (Q; 3,3',4',5,7 - pentahydroxyflavone) can help alleviate the pathological effects of nutritional obesity and metabolic syndrome when taken as part of products for special dietary needs and food supplements. The mechanisms of action of Q at the genetic level are not well understood.

AIMS

To study gene expression in liver tissue of mice with alimentary and genetically determined obesity upon intake of Q with diet.

MATERIALS AND METHODS

During 46 days of the experiment on 32 male C57Bl/6J mice fed a diet with an excess of fat and fructose and 24 male genetically obese db/db mice the effect of Q in dose of 25 or 100 mg/kg of body weight was studied on differential expression of 39430 genes in mice livers by full transcriptome profiling on microchip according to the Agilent One-Color Microarray-Based Gene Expression Analysis Low Input Quick Amp Labeling protocol (version 6.8). To identify metabolic pathways (KEGGs) that were targets of Q exposure, transcriptomic data were analyzed using bioinformatics methods in an "R" environment.

RESULTS

Differences were revealed in the nature of Q supplementation action in animals with dietary induced and genetically determined obesity on a number of key metabolic pathways, including the metabolism of lipids and steroids (Saa3, Cidec, Scd1, Apoa4, Acss2, Fabp5, Car3, Acacb, Insig2 genes), amino acids and nitrogen bases (Ngef, Gls2), carbohydrates (G6pdx, Pdk4), regulation of cell growth, apoptosis and proliferation (Btg3, Cgref1, Fst, Nrep Tuba8), neurotransmission (Grin2d, Camk2b), immune system reactions (CD14i, Jchain, Ifi27l2b).

CONCLUSIONS

The data obtained help to explain the ambiguous effectiveness of Q, like other polyphenols, in the dietary treatment of various forms of obesity in humans, as well as to form a set of sensitive biomarkers that allow us to elucidate the effectiveness of minor biologically active food substances in preclinical trials of new means of metabolic correction of obesity and metabolic syndrome.

Conditional Deletion of PGC-1α Results in Energetic and Functional Defects in NK Cells

During an immune response, natural killer (NK) cells activate specific metabolic pathways to meet the increased energetic and biosynthetic demands associated with effector functions. Here, we found in vivo activation of NK cells during Listeria monocytogenes infection-augmented transcription of genes encoding mitochondria-associated proteins in a manner dependent on the transcriptional coactivator PGC-1α. Using an Ncr1Cre-based conditional knockout mouse, we found that PGC-1α was crucial for optimal NK cell effector functions and bioenergetics, as the deletion of PGC-1α was associated with decreased cytotoxic potential and cytokine production along with altered ADP/ATP ratios. Lack of PGC-1α also significantly impaired the ability of NK cells to control B16F10 tumor growth in vivo, and subsequent gene expression analysis showed that PGC-1α mediates transcription required to maintain mitochondrial activity within the tumor microenvironment. Together, these data suggest that PGC-1α-dependent transcription of specific target genes is required for optimal NK cell function during the response to infection or tumor growth.

PPARδ and FOXO1 Mediate Palmitate-Induced Inhibition of Muscle Pyruvate Dehydrogenase Complex and CHO Oxidation, Events Reversed by Electrical Pulse Stimulation

The mechanisms behind the reduction in muscle pyruvate dehydrogenase complex (PDC)-controlled carbohydrate (CHO) oxidation during chronic high-fat dietary intake are poorly understood, as is the basis of CHO oxidation restoration during muscle contraction. C2C12 myotubes were treated with (300 μM) palmitate or without (control) for 16 h in the presence and absence of electrical pulse stimulation (EPS, 11.5 V, 1 Hz, 2 ms). Compared to control, palmitate reduced cell glucose uptake (p < 0.05), PDC activity (p < 0.01), acetylcarnitine accumulation (p < 0.05) and glucose-derived mitochondrial ATP production (p < 0.01) and increased pyruvate dehydrogenase kinase isoform 4 (PDK4) (p < 0.01), peroxisome proliferator-activated receptor alpha (PPARα) (p < 0.01) and peroxisome proliferator-activated receptor delta (PPARδ) (p < 0.01) proteins, and reduced the whole-cell p-FOXO1/t-FOXO1 (Forkhead Box O1) ratio (p < 0.01). EPS rescued palmitate-induced inhibition of CHO oxidation, reflected by increased glucose uptake (p < 0.01), PDC activity (p < 0.01) and glucose-derived mitochondrial ATP production (p < 0.01) compared to palmitate alone. EPS was also associated with less PDK4 (p < 0.01) and PPARδ (p < 0.01) proteins, and lower nuclear p-FOXO1/t-FOXO1 ratio normalised to the cytoplasmic ratio, but with no changes in PPARα protein. Collectively, these data suggest PPARδ, and FOXO1 transcription factors increased PDK4 protein in the presence of palmitate, which limited PDC activity and flux, and blunted CHO oxidation and glucose uptake. Conversely, EPS rescued these metabolic events by modulating the same transcription factors.

The Emerging Role of PPAR Beta/Delta in Tumor Angiogenesis

PPARs are ligand-activated transcriptional factors that belong to the nuclear receptor superfamily. Among them, PPAR alpha and PPAR gamma are prone to exert an antiangiogenic effect, whereas PPAR beta/delta has an opposite effect in physiological and pathological conditions. Angiogenesis has been known as a hallmark of cancer, and our recent works also demonstrate that vascular-specific PPAR beta/delta overexpression promotes tumor angiogenesis and progression in vivo. In this review, we will mainly focus on the role of PPAR beta/delta in tumor angiogenesis linked to the tumor microenvironment to further facilitate tumor progression and metastasis. Moreover, the crosstalk between PPAR beta/delta and its downstream key signal molecules involved in tumor angiogenesis will also be discussed, and the network of interplay between them will further be established in the review.

Integrated Analysis of Tissue-Specific Promoter Methylation and Gene Expression Profile in Complex Diseases

This study investigated whether the promoter region of DNA methylation positively or negatively regulates tissue-specific genes (TSGs) and if it correlates with disease pathophysiology. We assessed tissue specificity metrics in five human tissues, using sequencing-based approaches, including 52 whole genome bisulfite sequencing (WGBS), 52 RNA-seq, and 144 chromatin immunoprecipitation sequencing (ChIP-seq) data. A correlation analysis was performed between the gene expression and DNA methylation levels of the TSG promoter region. The TSG enrichment analyses were conducted in the gene-disease association network (DisGeNET). The epigenomic association analyses of CpGs in enriched TSG promoters were performed using 1986 Infinium MethylationEPIC array data. A correlation analysis showed significant associations between the promoter methylation and 449 TSGs' expression. A disease enrichment analysis showed that diabetes- and obesity-related diseases were high-ranked. In an epigenomic association analysis based on obesity, 62 CpGs showed statistical significance. Among them, three obesity-related CpGs were newly identified and replicated with statistical significance in independent data. In particular, a CpG (cg17075888 of PDK4), considered as potential therapeutic targets, were associated with complex diseases, including obesity and type 2 diabetes. The methylation changes in a substantial number of the TSG promoters showed a significant association with metabolic diseases. Collectively, our findings provided strong evidence of the relationship between tissue-specific patterns of epigenetic changes and metabolic diseases.

Genome-Wide Detection of Key Genes and Epigenetic Markers for Chicken Fatty Liver

Chickens are one of the most important sources of meat worldwide, and the occurrence of fatty liver syndrome (FLS) is closely related to production efficiency. However, the potential mechanism of FLS remains poorly understood. An integrated analysis of data from whole-genome bisulfite sequencing and long noncoding RNA (lncRNA) sequencing was conducted. A total of 1177 differentially expressed genes (DEGs) and 1442 differentially methylated genes (DMGs) were found. There were 72% of 83 lipid- and glucose-related genes upregulated; 81% of 150 immune-related genes were downregulated in fatty livers. Part of those genes was within differentially methylated regions (DMRs). Besides, sixty-seven lncRNAs were identified differentially expressed and divided into 13 clusters based on their expression pattern. Some lipid- and glucose-related lncRNAs (e.g., LNC_006756, LNC_012355, and LNC_005024) and immune-related lncRNAs (e.g., LNC_010111, LNC_010862, and LNC_001272) were found through a co-expression network and functional annotation. From the expression and epigenetic profiles, 23 target genes (e.g., HAO1, ABCD3, and BLMH) were found to be hub genes that were regulated by both methylation and lncRNAs. We have provided comprehensive epigenetic and transcriptomic profiles on FLS in chicken, and the identification of key genes and epigenetic markers will expand our understanding of the molecular mechanism of chicken FLS.

Functional Consequences of PDK4 Deficiency in Doberman Pinscher Fibroblasts

A splice site mutation in the canine pyruvate dehydrogenase kinase 4 (PDK4) gene has been shown to be associated with the development of dilated cardiomyopathy (DCM) in Doberman Pinchers (DPs). Subsequent studies have successfully demonstrated the use of dermal fibroblasts isolated from DPs as models for PDK4 deficiency and have shown activation of the intrinsic (mitochondrial mediated) apoptosis pathway in these cells under starvation conditions. For this study, we sought to further explore the functional consequences of PDK4 deficiency in DP fibroblasts representing PDK4^wt/wt, PDK4^wt/del, and PDK4^del/del genotypes. Our results show that starvation conditions cause increased perinuclear localization of mitochondria and decreased cell proliferation, altered expression levels of pyruvate dehydrogenase phosphatase (PDP) and pyruvate dehydrogenase (PDH), dramatically increased PDH activity, and an impaired response to mitochondrial stress in affected cells. In sum, these results show the broad impact of PDK4 deficiency and reveal mechanistic pathways used by these cells in an attempt to compensate for the condition. Our data help to elucidate the mechanisms at play in this extremely prevalent DP disorder and provide further support demonstrating the general importance of metabolic flexibility in cell health.

Vascular PPARβ/δ Promotes Tumor Angiogenesis and Progression

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors, which function as transcription factors. Among them, PPARβ/δ is highly expressed in endothelial cells. Pharmacological activation with PPARβ/δ agonists had been shown to increase their angiogenic properties. PPARβ/δ has been suggested to be involved in the regulation of the angiogenic switch in tumor progression. However, until now, it is not clear to what extent the expression of PPARβ/δ in tumor endothelium influences tumor progression and metastasis formation. We addressed this question using transgenic mice with an inducible conditional vascular-specific overexpression of PPARβ/δ. Following specific over-expression of PPARβ/δ in endothelial cells, we induced syngenic tumors. We observed an enhanced tumor growth, a higher vessel density, and enhanced metastasis formation in the tumors of animals with vessel-specific overexpression of PPARβ/δ. In order to identify molecular downstream targets of PPARβ/δ in the tumor endothelium, we sorted endothelial cells from the tumors and performed RNA sequencing. We identified platelet-derived growth factor receptor beta (Pdgfrb), platelet-derived growth factor subunit B (Pdgfb), and the tyrosinkinase KIT (c-Kit) as new PPARβ/δ -dependent molecules. We show here that PPARβ/δ activation, regardless of its action on different cancer cell types, leads to a higher tumor vascularization which favors tumor growth and metastasis formation.

Evaluation of the Anti-Diabetic Activity of Some Common Herbs and Spices: Providing New Insights with Inverse Virtual Screening

Culinary herbs and spices are widely used as a traditional medicine in the treatment of diabetes and its complications, and there are several scientific studies in the literature supporting the use of these medicinal plants. However, there is often a lack of knowledge on the bioactive compounds of these herbs and spices and their mechanisms of action. The aim of this study was to use inverse virtual screening to provide insights into the bioactive compounds of common herbs and spices, and their potential molecular mechanisms of action in the treatment of diabetes. In this study, a library of over 2300 compounds derived from 30 common herbs and spices were screened in silico with the DIA-DB web server against 18 known diabetes drug targets. Over 900 compounds from the herbs and spices library were observed to have potential anti-diabetic activity and liquorice, hops, fennel, rosemary, and fenugreek were observed to be particularly enriched with potential anti-diabetic compounds. A large percentage of the compounds were observed to be potential polypharmacological agents regulating three or more anti-diabetic drug targets and included compounds such as achillin B from yarrow, asparasaponin I from fenugreek, bisdemethoxycurcumin from turmeric, carlinoside from lemongrass, cinnamtannin B1 from cinnamon, crocin from saffron and glabridin from liquorice. The major targets identified for the herbs and spices compounds were dipeptidyl peptidase-4 (DPP4), intestinal maltase-glucoamylase (MGAM), liver receptor homolog-1 (NR5A2), pancreatic alpha-amylase (AM2A), peroxisome proliferator-activated receptor alpha (PPARA), protein tyrosine phosphatase non-receptor type 9 (PTPN9), and retinol binding protein-4 (RBP4) with over 250 compounds observed to be potential inhibitors of these particular protein targets. Only bay leaves, liquorice and thyme were found to contain compounds that could potentially regulate all 18 protein targets followed by black pepper, cumin, dill, hops and marjoram with 17 protein targets. In most cases more than one compound within a given plant could potentially regulate a particular protein target. It was observed that through this multi-compound-multi target regulation of these specific protein targets that the major anti-diabetic effects of reduced hyperglycemia and hyperlipidemia of the herbs and spices could be explained. The results of this study, taken together with the known scientific literature, indicated that the anti-diabetic potential of common culinary herbs and spices was the result of the collective action of more than one bioactive compound regulating and restoring several dysregulated and interconnected diabetic biological processes.

Genome-wide association analysis of egg production performance in chickens across the whole laying period

BACKGROUND

Egg production is the most economically-important trait in layers as it directly influences benefits of the poultry industry. To better understand the genetic architecture of egg production, we measured traits including age at first egg (AFE), weekly egg number (EN) from onset of laying eggs to 80 weeks which was divided into five stage (EN1: from onset of laying eggs to 23 weeks, EN2: from 23 to 37 weeks, EN3: from 37 to 50 weeks, EN4: from 50 to 61 weeks, EN5: from 61 to 80 weeks) based on egg production curve and total egg number across the whole laying period (Total-EN). Then we performed genome-wide association studies (GWAS) in 1078 Rhode Island Red hens using a linear mixed model.

RESULTS

Estimates of pedigree and SNP-based genetic parameter showed that AFE and EN1 exhibited high heritability (0.51 ± 0.09, 0.53 ± 0.08), while the h2 for EN in other stages varied from low (0.07 ± 0.04) to moderate (0.24 ± 0.07) magnitude. Subsequently, seven univariate GWAS for AFE and ENs were carried out independently, from which a total of 161 candidate SNPs located on GGA1, GGA2, GGA5, GGA6, GGA9 and GGA24 were identified. Thirteen SNP located on GGA6 were associated with AFE and an interesting gene PRLHR that may affect AFE through regulating oxytocin secretion in chickens. Sixteen genome-wide significant SNPs associated with EN3 were in a strong linkage disequilibrium (LD) region spanning from 117.87 Mb to 118.36 Mb on GGA1 and the most significant SNP (rs315777735) accounted for 3.57% of phenotypic variance. Genes POLA1, PDK3, PRDX4 and APOO identified by annotating sixteen genome-wide significant SNPs can be considered as candidates associated with EN3. Unfortunately, our study did not find any candidate gene for the total egg number.

CONCLUSIONS

Findings in our study could provide promising genes and SNP markers to improve egg production performance based on marker-assisted breeding selection, while further functional validation is still needed in other populations.

Increase in muscle endurance in mice by dietary Yamabushitake mushroom (Hericium erinaceus) possibly via activation of PPARδ

Skeletal muscle fiber is largely classified into two types: type 1 (slow‐twitch) and type 2 (fast‐twitch) fibers. Meat quality and composition of fiber types are thought to be closely related. Previous research showed that overexpression of constitutively active peroxisome proliferator‐activated receptor (PPAR)δ, a nuclear receptor present in skeletal muscle, increased type 1 fibers in mice. In this study, we found that hexane extracts of Yamabushitake mushroom (Hericium erinaceus) showed PPARδ agonistic activity in vitro. Eight‐week‐old C57BL/6J mice were fed a diet supplemented with 5% (w/w) freeze‐dried Yamabushitake mushroom for 24 hr. After the treatment period, the extensor digitorum longus (EDL) muscles were excised. The Yamabushitake‐supplemented diet up‐regulated the PPARδ target genes Pdk4 and Ucp3 in mouse skeletal muscles in vivo. Furthermore, feeding the Yamabushitake‐supplemented diet to mice for 8 weeks resulted in a significant increase in muscle endurance. These results indicate that Yamabushitake mushroom contains PPARδ agonistic ligands and that dietary intake of Yamabushitake mushroom could activate PPARδ in skeletal muscle of mice. Unexpectedly, we observed no significant alterations in composition of muscle fiber types between the mice fed control and Yamabushitake‐supplemented diets.

PDK4 drives metabolic alterations and muscle atrophy in cancer cachexia

Cachexia is frequently accompanied by severe metabolic derangements, although the mechanisms responsible for this debilitating condition remain unclear. Pyruvate dehydrogenase kinase (PDK)4, a critical regulator of cellular energetic metabolism, was found elevated in experimental models of cancer, starvation, diabetes, and sepsis. Here we aimed to investigate the link between PDK4 and the changes in muscle size in cancer cachexia. High PDK4 and abnormal energetic metabolism were found in the skeletal muscle of colon-26 tumor hosts, as well as in mice fed a diet enriched in Pirinixic acid, previously shown to increase PDK4 levels. Viral-mediated PDK4 overexpression in myotube cultures was sufficient to promote myofiber shrinkage, consistent with enhanced protein catabolism and mitochondrial abnormalities. On the contrary, blockade of PDK4 was sufficient to restore myotube size in C2C12 cultures exposed to tumor media. Our data support, for the first time, a direct role for PDK4 in promoting cancer-associated muscle metabolic alterations and skeletal muscle atrophy.-Pin, F., Novinger, L. J., Huot, J. R., Harris, R. A., Couch, M. E., O'Connell, T. M., Bonetto, A. PDK4 drives metabolic alterations and muscle atrophy in cancer cachexia.

Adaptations in Protein Expression and Regulated Activity of Pyruvate Dehydrogenase Multienzyme Complex in Human Systolic Heart Failure

Pyruvate dehydrogenase (PDH) complex, a multienzyme complex at the nexus of glycolytic and Krebs cycles, provides acetyl-CoA to the Krebs cycle and NADH to complex I thus supporting a critical role in mitochondrial energy production and cellular survival. PDH activity is regulated by pyruvate dehydrogenase phosphatases (PDP1, PDP2), pyruvate dehydrogenase kinases (PDK 1-4), and mitochondrial pyruvate carriers (MPC1, MPC2). As NADH-dependent oxidative phosphorylation is diminished in systolic heart failure, we tested whether the left ventricular myocardium (LV) from end-stage systolic adult heart failure patients (n = 26) exhibits altered expression of PDH complex subunits, PDK, MPC, PDP, and PDH complex activity, compared to LV from nonfailing donor hearts (n = 21). Compared to nonfailing LV, PDH activity and relative expression levels of E2, E3bp, E1α, and E1β subunits were greater in LV failure. PDK4, MPC1, and MPC2 expressions were decreased in failing LV, whereas PDP1, PDP2, PDK1, and PDK2 expressions did not differ between nonfailing and failing LV. In order to examine PDK4 further, donor human LV cardiomyocytes were induced in culture to hypertrophy with 0.1 μM angiotensin II and treated with PDK inhibitors (0.2 mM dichloroacetate, or 5 mM pyruvate) or activators (0.6 mM NADH plus 50 μM acetyl CoA). In isolated hypertrophic cardiomyocytes in vitro, PDK activators and inhibitors increased and decreased PDK4, respectively. In conclusion, in end-stage failing hearts, greater expression of PDH proteins and decreased expression of PDK4, MPC1, and MPC2 were evident with higher rates of PDH activity. These adaptations support sustained capacity for PDH to facilitate glucose metabolism in the face of other failing bioenergetic pathways.

PPARδ, a Potential Therapeutic Target for Heart Disease

The nuclear receptor peroxisome proliferator-activated receptor δ (PPARδ) can transcriptionally regulate target genes. PPARδ exerts essential regulatory functions in the heart, which requires constant energy supply. PPARδ plays a key role in energy metabolism, controlling not only fatty acid (FA) and glucose oxidation, but also redox homeostasis, mitochondrial biogenesis, inflammation, and cardiomyocyte proliferation. PPARδ signaling is impaired in the heart under various pathological conditions, such as pathological cardiac hypertrophy, myocardial ischemia/reperfusion, doxorubicin cardiotoxicity and diabetic cardiomyopathy. PPARδ deficiency in the heart leads to cardiac dysfunction, myocardial lipid accumulation, cardiac hypertrophy/remodeling and heart failure. This article provides an up-today overview of this research area and discusses the role of PPARδ in the heart in light of the complex mechanisms of its transcriptional regulation and its potential as a translatable therapeutic target for the treatment of cardiac disorders.

An aPPARent Functional Consequence in Skeletal Muscle Physiology via Peroxisome Proliferator-Activated Receptors

Skeletal muscle comprises 30–40% of the total body mass and plays a central role in energy homeostasis in the body. The deregulation of energy homeostasis is a common underlying characteristic of metabolic syndrome. Over the past decades, peroxisome proliferator-activated receptors (PPARs) have been shown to play critical regulatory roles in skeletal muscle. The three family members of PPAR have overlapping roles that contribute to the myriad of processes in skeletal muscle. This review aims to provide an overview of the functions of different PPAR members in energy homeostasis as well as during skeletal muscle metabolic disorders, with a particular focus on human and relevant mouse model studies.

Central leptin regulates heart lipid content by selectively increasing PPAR β/δ expression

The role of central leptin in regulating the heart from lipid accumulation in lean leptin-sensitive animals has not been fully elucidated. Herein, we investigated the effects of central leptin infusion on the expression of genes involved in cardiac metabolism and its role in the control of myocardial triacylglyceride (TAG) accumulation in adult Wistar rats. Intracerebroventricular (icv) leptin infusion (0.2 µg/day) for 7 days markedly decreased TAG levels in cardiac tissue. Remarkably, the cardiac anti-steatotic effects of central leptin were associated with the selective upregulation of gene and protein expression of peroxisome proliferator-activated receptor β/δ (PPARβ/δ, encoded by Pparb/d) and their target genes, adipose triglyceride lipase (encoded by Pnpla2, herefater referred to as Atgl), hormone sensitive lipase (encoded by Lipe, herefater referred to as Hsl), pyruvate dehydrogenase kinase 4 (Pdk4) and acyl CoA oxidase 1 (Acox1), involved in myocardial intracellular lipolysis and mitochondrial/peroxisomal fatty acid utilization. Besides, central leptin decreased the expression of stearoyl-CoA deaturase 1 (Scd1) and diacylglycerol acyltransferase 1 (Dgat1) involved in TAG synthesis and increased the CPT-1 independent palmitate oxidation, as an index of peroxisomal β-oxidation. Finally, the pharmacological inhibition of PPARβ/δ decreased the effects on gene expression and cardiac TAG content induced by leptin. These results indicate that leptin, acting at central level, regulates selectively the cardiac expression of PPARβ/δ, contributing in this way to regulate the cardiac TAG accumulation in rats, independently of its effects on body weight.

Reversal of Defective Mitochondrial Biogenesis in Limb-Girdle Muscular Dystrophy 2D by Independent Modulation of Histone and PGC-1α Acetylation

Mitochondrial dysfunction occurs in many muscle degenerative disorders. Here, we demonstrate that mitochondrial biogenesis was impaired in limb-girdle muscular dystrophy (LGMD) 2D patients and mice and was associated with impaired OxPhos capacity. Two distinct approaches that modulated histones or peroxisome proliferator-activated receptor-gamma coactivator 1 α (PGC-1α) acetylation exerted equivalent functional effects by targeting different mitochondrial pathways (mitochondrial biogenesis or fatty acid oxidation[FAO]). The histone deacetylase inhibitor Trichostatin A (TSA) changed chromatin assembly at the PGC-1α promoter, restored mitochondrial biogenesis, and enhanced muscle oxidative capacity. Conversely, nitric oxide (NO) triggered post translation modifications of PGC-1α and induced FAO, recovering the bioenergetics impairment of muscles but shunting the defective mitochondrial biogenesis. In conclusion, a transcriptional blockade of mitochondrial biogenesis occurred in LGMD-2D and could be recovered by TSA changing chromatin conformation, or it could be overcome by NO activating a mitochondrial salvage pathway.

Mitochondrial Bioenergetics and Dysfunction in Failing Heart

Energy insufficiency has been recognized as a key feature of systolic heart failure. Although mitochondria have long been known to sustain myocardial work energy supply, the capacity to therapeutically target mitochondrial bioenergetics dysfunction is hampered by a complex interplay of multiple perturbations that progressively compound causing myocardial failure and collapse. Compared to non-failing human donor hearts, activity rates of complexes I and IV, nicotinamide nucleotide transhydrogenase (NADPH-transhydrogenase, Nnt) and the Krebs cycle enzymes isocitrate dehydrogenase, malate dehydrogenase and aconitase are markedly decreased in end-stage heart failure. Diminished REDOX capacity with lower total glutathione and coenzyme Q₁₀ levels are also a feature of chronic left ventricular failure. Decreased enzyme activities in part relate to abundant and highly specific oxidative, nitrosylative, and hyperacetylation modifications. In this brief review we highlight that energy deficiency in end-stage failing human left ventricle predominantly involves concomitantly impaired activities of key electron transport chain and Krebs cycle enzymes rather than altered expression of respective genes or proteins. Augmented oxidative modification of these enzyme subunit structures, and the formation of highly reactive secondary metabolites, implicates dysfunction due to diminished capacity for management of mitochondrial reactive oxygen species, which contribute further to progressive decreases in bioenergetic capacity and contractile function in human heart failure.

PPARβ/δ in human cancer

The nuclear receptor factor peroxisome proliferator-activated receptor (PPARβ/δ) can regulate its target genes by transcriptional activation or repression through both ligand-dependent and independent mechanism as well as by interactions with other transcription factors. PPARβ/δ exerts essential regulatory functions in intermediary metabolism that have been elucidated in detail, but clearly also plays a role in inflammation, differentiation, apoptosis and other cancer-associated processes, which is, however, mechanistically only partly understood. Consistent with these functions clinical associations link the expression of PPARβ/δ and its target genes to an unfavorable outcome of several human cancers. However, the available data do not yield a clear picture of PPARβ/δ's role in cancer-associated processes and are in fact partly controversial. This article provides an overview of this research area and discusses the role of PPARβ/δ in cancer in light of the complex mechanisms of its transcriptional regulation and its potential as a druggable anti-cancer target.

Vascular smooth muscle cell dysfunction in diabetes: nuclear receptors channel to relaxation

Endothelial dysfunction and impaired vascular relaxation represent a common cause of microvascular disease in patients with diabetes. Although multiple mechanisms underlying altered endothelial cell function in diabetes have been described, there is currently no specific and approved pharmacological treatment. In this edition of Clinical Science, Morales-Cano et al. characterize voltage-dependent K+ (Kv) channels as genes regulated by pharmacological activation of peroxisome proliferator-activated receptor-b/d (PPARb/d). Diabetes altered Kv channel function leading to impaired coronary artery relaxation, which was prevented by pharmacological activation of PPARb/d. These studies highlight an important mechanism of vascular dysfunction in diabetes and point to a potential approach for therapy, particularly considering that PPARb/d ligands have been developed and tested in small clinical trials.

Activation of PPARβ/δ prevents hyperglycaemia-induced impairment of Kv7 channels and cAMP-mediated relaxation in rat coronary arteries

PPARβ/δ activation protects against endothelial dysfunction in diabetic models. Elevated glucose is known to impair cAMP-induced relaxation and Kv channel function in coronary arteries (CA). Herein, we aimed to analyse the possible protective effects of the PPARβ/δ agonist GW0742 on the hyperglycaemic-induced impairment of cAMP-induced relaxation and Kv channel function in rat CA. As compared with low glucose (LG), incubation under high glucose (HG) conditions attenuated the relaxation induced by the adenylate cyclase activator forskolin in CA and this was prevented by GW0742. The protective effect of GW0742 was supressed by a PPARβ/δ antagonist. In myocytes isolated from CA under LG, forskolin enhanced Kv currents and induced hyperpolarization. In contrast, when CA were incubated with HG, Kv currents were diminished and the electrophysiological effects of forskolin were abolished. These deleterious effects were prevented by GW0742. The protective effects of GW0742 on forskolin-induced relaxation and Kv channel function were confirmed in CA from type-1 diabetic rats. In addition, the differences in the relaxation induced by forskolin in CA incubated under LG, HG or HG + GW0742 were abolished by the Kv7 channel inhibitor XE991. Accordingly, GW0742 prevented the down-regulation of Kv7 channels induced by HG. Finally, the preventive effect of GW0742 on oxidative stress and cAMP-induced relaxation were overcome by the pyruvate dehydrogenase kinase 4 (PDK4) inhibitor dichloroacetate (DCA). Our results reveal that the PPARβ/δ agonist GW0742 prevents the impairment of the cAMP-mediated relaxation in CA under HG. This protective effect was associated with induction of PDK4, attenuation of oxidative stress and preservation of Kv7 channel function.

Picrasidine N Is a Subtype-Selective PPARβ/δ Agonist

Recently, growing evidence of the pivotal roles of peroxisome proliferator-activated receptor (PPAR) β/δ in various physiological functions, including lipid homeostasis, cancer, and inflammation, has raised interest in this receptor. In this study, the naturally occurring dimeric alkaloid picrasidine N (1) from Picrasma quassioides was identified as a novel PPARβ/δ agonist from a library consisting of plant extracts and natural compounds using a mammalian one-hybrid assay, and this compound was characterized. Compound 1 activated PPARβ/δ but did not activate or slightly activated PPARα and PPARγ. Furthermore, a peroxisome proliferator response element-driven luciferase reporter gene assay demonstrated that 1 enhanced PPARβ/δ transcriptional activity. Moreover, 1 selectively induced mRNA expression of ANGPTL4, which is a PPAR target gene. This observation is quite different from previously identified synthetic PPARβ/δ agonists, which can induce the expression of not only ANGPTL4 but also other PPAR target genes, such as ADRP, PDK4, and CPT-1. These results demonstrate that 1 is a potent subtype-selective and gene-selective PPARβ/δ agonist, suggesting its potential as a lead compound for further drug development. This compound would also be a useful chemical tool for elucidating the mechanism of PPARβ/δ-regulated specific gene expression and the biological significance of PPARβ/δ.

Deregulation of PPARβ/δ target genes in tumor-associated macrophages by fatty acid ligands in the ovarian cancer microenvironment

The nuclear receptor peroxisome proliferator-activated receptor β/δ (PPARβ/δ) is a lipid ligand-inducible transcription factor associated with macrophage polarization. However, its function in tumor-associated macrophages (TAMs) has not been investigated to date. Here, we report the PPARβ/δ-regulated transcriptome and cistrome for TAMs from ovarian carcinoma patients. Comparison with monocyte-derived macrophages shows that the vast majority of direct PPARβ/δ target genes are upregulated in TAMs and largely refractory to synthetic agonists, but repressible by inverse agonists. Besides genes with metabolic functions, these include cell type-selective genes associated with immune regulation and tumor progression, e.g., LRP5, CD300A, MAP3K8 and ANGPTL4. This deregulation is not due to increased expression of PPARβ/δ or its enhanced recruitment to target genes. Instead, lipidomic analysis of malignancy-associated ascites revealed high concentrations of polyunsaturated fatty acids, in particular linoleic acid, acting as potent PPARβ/δ agonists in macrophages. These fatty acid ligands accumulate in lipid droplets in TAMs, thereby providing a reservoir of PPARβ/δ ligands. These observations suggest that the deregulation of PPARβ/δ target genes by ligands of the tumor microenvironment contributes to the pro-tumorigenic polarization of ovarian carcinoma TAMs. This conclusion is supported by the association of high ANGPTL4 expression with a shorter relapse-free survival in serous ovarian carcinoma.

ReMo-SNPs: a new software tool for identification of polymorphisms in regions and motifs genome-wide

Studies of complex genetic diseases have revealed many risk factors of small effect, but the combined amount of heritability explained is still low. Genome-wide association studies are often underpowered to identify true effects because of the very large number of parallel tests. There is, therefore, a great need to generate data sets that are enriched for those markers that have an increased a priori chance of being functional, such as markers in genomic regions involved in gene regulation. ReMo-SNPs is a computational program developed to aid researchers in the process of selecting functional SNPs for association analyses in user-specified regions and/or motifs genome-wide. The useful feature of automatic selection of genotyped markers in the user-provided material makes the output data ready to be used in a following association study. In this article we describe the program and its functions. We also validate the program by including an example study on three different transcription factors and results from an association study on two psychiatric phenotypes. The flexibility of the ReMo-SNPs program enables the user to study any region or sequence of interest, without limitation to transcription factor binding regions and motifs. The program is freely available at: http://www.neuro.ki.se/ReMo-SNPs/.

PPARβ activation restores the high glucose-induced impairment of insulin signalling in endothelial cells

BACKGROUND AND PURPOSE

PPARβ enhances insulin sensitivity in adipocytes and skeletal muscle cells, but its effects on insulin signalling in endothelial cells are not known. We analysed the effects of the PPARβ/δ (PPARβ) agonists, GW0742 and L165041, on impaired insulin signalling induced by high glucose in HUVECs and aortic and mesenteric arteries from diabetic rats.

EXPERIMENTAL APPROACH

Insulin-stimulated NO production, Akt-Ser(473) and eNOS-Ser(1177) phosphorylation, and reactive oxygen species (ROS) production were studied in HUVECs incubated in low- or high-glucose medium. Insulin-stimulated relaxations and protein phosphorylation in vessels from streptozotocin (STZ)-induced diabetic rats were also analysed.

KEY RESULTS

HUVECs incubated in high-glucose medium showed a significant reduction in insulin-stimulated production of NO. High glucose also reduced insulin-induced Akt-Ser(473) and eNOS-Ser(1177) phosphorylation, increased IRS-1-Ser(636) and ERK1/2-Thr(183) -Tyr(185) phosphorylation and increased ROS production. The co-incubation with the PPARβ agonists GW0742 or L165041 prevented all these effects induced by high glucose. In turn, the effects induced by the agonists were suppressed when HUVEC were also incubated with the PPARβ antagonist GSK0660, the pyruvate dehydrogenase kinase (PDK)4 inhibitor dichloroacetate or after knockdown of both PPARβ and PDK4 with siRNA. The ERK1/2 inhibitor PD98059, ROS scavenger catalase, inhibitor of complex II thenoyltrifluoroacetone or uncoupler of oxidative phosphorylation, carbonyl cyanide m-chlorophenylhydrazone, also prevented glucose-induced insulin resistance. In STZ diabetic rats, oral GW0742 also improved insulin signalling and the impaired NO-mediated vascular relaxation.

CONCLUSION AND IMPLICATIONS

PPARβ activation in vitro and in vivo restores the endothelial function, preserving the insulin-Akt-eNOS pathway impaired by high glucose, at least in part, through PDK4 activation.

Curcumin restores sensitivity to retinoic acid in triple negative breast cancer cells

Background

A major obstacle in the use of retinoid therapy in cancer is the resistance to this agent in tumors. Retinoic acid facilitates the growth of mammary carcinoma cells which express high levels of fatty acid-binding protein 5 (FABP5). This protein delivers retinoic acid to peroxisome proliferator-activated receptor β/δ (PPARβ/δ) that targets genes involved in cell proliferation and survival. One approach to overcome resistance of mammary carcinoma cells to retinoic acid is to target and suppress the FABP5/ PPARβ/δ pathway. The objective of this research was to investigate the effect of curcumin, a polyphenol extract from the plant Curcuma longa, on the FABP5/ PPARβ/δ pathway in retinoic acid resistant triple negative breast cancer cells.

Methods

Cell viability and proliferation of triple negative breast cancer cell lines (MDA-MB-231 and MD-MB-468) treated with curcumin and/or retinoic was analyzed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and 5-bromo-2’-deoxyuridine (BrdU). Expression level of FABP5 and PPARβ/δ in these cells treated with curcumin was examined by Western Blotting analysis and Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR). Effect of curcumin and retinoic acid on PPARβ/δ target genes, PDK1and VEGF-A were also examined using qRT-PCR. Western Blotting was utilized to examine the protein expression level of the p65 subunit of NF-κB.

Results

Treatment of retinoic acid resistant triple negative breast cancer cells with curcumin sensitized these cells to retinoic acid mediated growth suppression, as well as suppressed incorporation of BrdU. Further studies demonstrated that curcumin showed a marked reduction in the expression level of FABP5 and PPARβ/δ. We provide evidence that curcumin suppresses p65, a transcription factor known to regulate FABP5. The combination of curcumin with retinoic acid suppressed PPARβ/δ target genes, VEGF-A and PDK1.

Conclusions

Curcumin suppresses the expression level of FABP5 and PPARβ/δ in triple negative mammary carcinoma cells. By targeting the FABP5/PPARβ/δ pathway, curcumin prevents the delivery of retinoic acid to PPARβ/δ and suppresses retinoic acid-induced PPARβ/δ target gene, VEGF-A. Our data demonstrates that suppression of the FABP5/ PPARβ/δ pathway by curcumin sensitizes retinoic acid resistant triple negative breast cancer cells to retinoic acid mediated growth suppression.

Activation of PPAR α and PPAR β/δ regulates Sertoli cell metabolism

The purpose of this study was to evaluate the existence of a possible simultaneous regulation of fatty acid (FA) metabolism and lactate production by PPAR α and PPAR β/δ activation in Sertoli cells (SC). SC cultures obtained from 20-day-old rats were incubated with WY14643 or GW0742-pharmacological activators of PPAR α and PPAR β/δ respectively. The fatty acid transporter CD36, carnitine palmitoyltransferase 1, long- and medium-chain 3-hydroxyacyl-CoA dehydrogenases mRNA levels were analyzed. An increase in the above-mentioned genes in response to activation of both nuclear receptors was observed. Additionally, PPAR β/δ activation increased lactate production as a consequence of increased pyruvate availability by inhibiting the Pyruvate Dehydrogenase Complex. Altogether, these results suggest that in SC, PPAR α activation participates in the regulation of FA metabolism. On the other hand, PPAR β/δ activation regulates FA metabolism and lactate production ensuring simultaneously the energetic metabolism for SC and germ cells.

Small molecule agonists of PPAR-γ exert therapeutic effects in esophageal cancer

The transcription factor PPAR-γ plays various roles in lipid metabolism, inflammation, cellular differentiation, and apoptosis. PPAR-γ agonists used to treat diabetes may have utility in cancer treatment. Efatutazone is a novel later generation PPAR-γ agonist that selectively activates PPAR-γ target genes and has antiproliferative effects in a range of malignancies. In this study, we investigated PPAR-γ status in esophageal squamous cell carcinoma (ESCC) and investigated the antiproliferative effects of efatutazone. PPAR-γ was expressed heterogeneously in ESCC, in which it exhibited an inverse relationship with Ki-67 expression. PPAR-γ expression was associated independently with good prognosis in ESCC. Efatutazone, but not the conventional PPAR-γ agonist troglitazone, inhibited ESCC cell proliferation in vitro and in vivo. Mechanistic investigations suggested that efatutazone acted by upregulating p21Cip1 protein in the nucleus through inactivation of the Akt pathway and dephosphorylation of p21Cip1 at Thr145 without affecting the transcriptional activity of p21Cip1. We also found that treatment with efatutazone led to phosphorylation of the EGF receptor and activation of the mitogen-activated protein kinase (MAPK) pathway. Accordingly, the combination of efatutazone with the antiepithelial growth factor receptor antibody cetuximab synergized to negatively regulate the phosphoinositide 3-kinase-Akt and MAPK pathways. Together, our results suggest that efatutazone, alone or in combination with cetuximab, may offer therapeutic effects in ESCC.

Genetic dissection of retinoid esterification and accumulation in the liver and adipose tissue

Approximately 80-90% of all retinoids in the body are stored as retinyl esters (REs) in the liver. Adipose tissue also contributes significantly to RE storage. The present studies, employing genetic and nutritional interventions, explored factors that are responsible for regulating RE accumulation in the liver and adipose tissue and how these influence levels of retinoic acid (RA) and RA-responsive gene expression. Our data establish that acyl-CoA:retinol acyltransferase (ARAT) activity is not involved in RE synthesis in the liver, even when mice are nutritionally stressed by feeding a 25-fold excess retinol diet or upon ablation of cellular retinol-binding protein type I (CRBPI), which is proposed to limit retinol availability to ARATs. Unlike the liver, where lecithin:retinol acyltransferase (LRAT) is responsible for all RE synthesis, this is not true for adipose tissue where Lrat-deficient mice display significantly elevated RE concentrations. However, when CrbpI is also absent, RE levels resemble wild-type levels, suggesting a role for CrbpI in RE accumulation in adipose tissue. Although expression of several RA-responsive genes is elevated in Lrat-deficient liver, employing a sensitive liquid chromatography tandem mass spectrometry protocol and contrary to what has been assumed for many years, we did not detect elevated concentrations of all-trans-RA. The elevated RA-responsive gene expression was associated with elevated hepatic triglyceride levels and decreased expression of Pparδ and its downstream Pdk4 target, suggesting a role for RA in these processes in vivo.

Regulation of muscle pyruvate dehydrogenase complex in insulin resistance: effects of exercise and dichloroacetate

Since the mitochondrial pyruvate dehydrogenase complex (PDC) controls the rate of carbohydrate oxidation, impairment of PDC activity mediated by high-fat intake has been advocated as a causative factor for the skeletal muscle insulin resistance, metabolic syndrome, and the onset of type 2 diabetes (T2D). There are also situations where muscle insulin resistance can occur independently from high-fat dietary intake such as sepsis, inflammation, or drug administration though they all may share the same underlying mechanism, i.e., via activation of forkhead box family of transcription factors, and to a lower extent via peroxisome proliferator-activated receptors. The main feature of T2D is a chronic elevation in blood glucose levels. Chronic systemic hyperglycaemia is toxic and can lead to cellular dysfunction that may become irreversible over time due to deterioration of the pericyte cell's ability to provide vascular stability and control to endothelial proliferation. Therefore, it may not be surprising that T2D's complications are mainly macrovascular and microvascular related, i.e., neuropathy, retinopathy, nephropathy, coronary artery, and peripheral vascular diseases. However, life style intervention such as exercise, which is the most potent physiological activator of muscle PDC, along with pharmacological intervention such as administration of dichloroacetate or L-carnitine can prove to be viable strategies for treating muscle insulin resistance in obesity and T2D as they can potentially restore whole body glucose disposal.

Myelin alters the inflammatory phenotype of macrophages by activating PPARs

Background

Foamy macrophages, containing myelin degradation products, are abundantly found in active multiple sclerosis (MS) lesions. Recent studies have described an altered phenotype of macrophages after myelin internalization. However, mechanisms by which myelin affects the phenotype of macrophages and how this phenotype influences lesion progression remain unclear.

Results

We demonstrate that myelin as well as phosphatidylserine (PS), a phospholipid found in myelin, reduce nitric oxide production by macrophages through activation of peroxisome proliferator-activated receptor β/δ (PPARβ/δ). Furthermore, uptake of PS by macrophages, after intravenous injection of PS-containing liposomes (PSLs), suppresses the production of inflammatory mediators and ameliorates experimental autoimmune encephalomyelitis (EAE), an animal model of MS. The protective effect of PSLs in EAE animals is associated with a reduced immune cell infiltration into the central nervous system and decreased splenic cognate antigen specific proliferation. Interestingly, PPARβ/δ is activated in foamy macrophages in active MS lesions, indicating that myelin also activates PPARβ/δ in macrophages in the human brain.

Conclusion

Our data show that myelin modulates the phenotype of macrophages by PPAR activation, which may subsequently dampen MS lesion progression. Moreover, our results suggest that myelin-derived PS mediates PPARβ/δ activation in macrophages after myelin uptake. The immunoregulatory impact of naturally-occurring myelin lipids may hold promise for future MS therapeutics.

HIV-1 Vpr enhances PPARβ/δ-mediated transcription, increases PDK4 expression, and reduces PDC activity

HIV infection and its therapy are associated with disorders of lipid metabolism and bioenergetics. Previous work has suggested that viral protein R (Vpr) may contribute to the development of lipodystrophy and insulin resistance observed in HIV-1-infected patients. In adipocytes, Vpr suppresses mRNA expression of peroxisomal proliferator-activating receptor-γ (PPARγ)-responsive genes and inhibits differentiation. We investigated whether Vpr might interact with PPARβ/δ and influence its transcriptional activity. In the presence of PPARβ/δ, Vpr induced a 3.3-fold increase in PPAR response element-driven transcriptional activity, a 1.9-fold increase in pyruvate dehydrogenase kinase 4 (PDK4) protein expression, and a 1.6-fold increase in the phosphorylated pyruvate dehydrogenase subunit E1α leading to a 47% decrease in the activity of the pyruvate dehydrogenase complex in HepG2 cells. PPARβ/δ knockdown attenuated Vpr-induced enhancement of endogenous PPARβ/δ-responsive PDK4 mRNA expression. Vpr induced a 1.3-fold increase in mRNA expression of both carnitine palmitoyltransferase I (CPT1) and acetyl-coenzyme A acyltransferase 2 (ACAA2) and doubled the activity of β-hydroxylacyl coenzyme A dehydrogenase (HADH). Vpr physically interacted with the ligand-binding domain of PPARβ/δ in vitro and in vivo. Consistent with a role in energy expenditure, Vpr increased state-3 respiration in isolated mitochondria (1.16-fold) and basal oxygen consumption rate in intact HepG2 cells (1.2-fold) in an etomoxir-sensitive manner, indicating that the oxygen consumption rate increase is β-oxidation-dependent. The effects of Vpr on PPAR response element activation, pyruvate dehydrogenase complex activity, and β-oxidation were reversed by specific PPARβ/δ antagonists. These results support the hypothesis that Vpr contributes to impaired energy metabolism and increased energy expenditure in HIV patients.

A new locus for X-linked dominant Charcot-Marie-Tooth disease (CMTX6) is caused by mutations in the pyruvate dehydrogenase kinase isoenzyme 3 (PDK3) gene

Hereditary motor and sensory disorders of the peripheral nerve form one of the most common groups of human genetic diseases collectively called Charcot-Marie-Tooth (CMT) neuropathy. Using linkage analysis in a three generation kindred, we have mapped a new locus for X-linked dominant CMT to chromosome Xp22.11. A microsatellite scan of the X chromosome established significant linkage to several markers including DXS993 (Zmax = 3.16; θ = 0.05). Extended haplotype analysis refined the linkage region to a 1.43-Mb interval flanked by markers DXS7110 and DXS8027. Whole exome sequencing identified a missense mutation c.G473A (p.R158H) in the pyruvate dehydrogenase kinase isoenzyme 3 (PDK3) gene. The change localized within the 1.43-Mb linkage interval, segregated with the affected phenotype and was excluded in ethnically matched control chromosomes. PDK3 is one of the four isoenzymes regulating the pyruvate dehydrogenase complex (PDC), by reversible phosphorylation, and is a nuclear-coded protein located in the mitochondrial matrix. PDC catalyzes the oxidative decarboxylation of pyruvate to acetyl CoA and is a key enzyme linking glycolysis to the energy-producing Krebs cycle and lipogenic pathways. We found that the R158H mutation confers enzyme hyperactivity and binds with stronger affinity than the wild-type to the inner-lipoyl (L2) domain of the E2p chain of PDC. Our findings suggest a reduced pyruvate flux due to R158H mutant PDK3-mediated hyper-phosphorylation of the PDC as the underlying pathogenic cause of peripheral neuropathy. The results highlight an important causative link between peripheral nerve degeneration and an essential bioenergetic or biosynthetic pathway required for the maintenance of peripheral nerves.

Influence of beta-blockers on the myocardial mRNA expressions of circadian clock- and metabolism-related genes

Daily rhythms are regulated by a master clock-system in the suprachiasmatic nucleus and by a peripheral clock-system in each organ. Because norepinephrine is one of the timekeepers for the myocardial circadian clock that influences cardiac metabolism, it is speculated that a beta-blocker may affect the circadian clock and metabolism in heart tissue. In this study, thirty mg/kg/day of propranolol (a lipophilic beta-blocker) or atenolol (a hydrophilic beta-blocker) was given orally to Wistar rats for 4 weeks. The mRNA expressions of Bmal1 and E4BP4 in heart tissue were suppressed by the beta-blockers. However, the mRNA expressions of these clock genes in the suprachiasmatic nucleus were unchanged. Myocardial mRNA expressions of lactate dehydrogenase a and pyruvate dehydrogenase kinase 4 were also suppressed by the beta-blockers. In addition, ATP content in heart tissue was significantly elevated by the beta-blockers throughout 24 hours. The effects of propranolol and atenolol did not differ significantly. This study showed for the first time that a beta-blocker affects myocardial clock gene expression. Propranolol and atenolol increased ATP content in heart tissue throughout 24 hours. The influences of beta-blockers may be negligible on the SCN, and may be independent of lipid solubility on heart tissue. It is well known that these drugs exert a protective effect against myocardial ischemia, which may be mediated by an increase in the preservation of myocardial ATP.

Transcriptional regulation of pyruvate dehydrogenase kinase

The pyruvate dehydrogenase complex (PDC) activity is crucial to maintains blood glucose and ATP levels, which largely depends on the phosphorylation status by pyruvate dehydrogenase kinase (PDK) isoenzymes. Although it has been reported that PDC is phosphorylated and inactivated by PDK2 and PDK4 in metabolically active tissues including liver, skeletal muscle, heart, and kidney during starvation and diabetes, the precise mechanisms by which expression of PDK2 and PDK4 are transcriptionally regulated still remains unclear. Insulin represses the expression of PDK2 and PDK4 via phosphorylation of FOXO through PI3K/Akt signaling pathway. Several nuclear hormone receptors activated due to fasting or increased fat supply, including peroxisome proliferator-activated receptors, glucocorticoid receptors, estrogen-related receptors, and thyroid hormone receptors, also participate in the up-regulation of PDK2 and PDK4; however, the endogenous ligands that bind those nuclear receptors have not been identified. It has been recently suggested that growth hormone, adiponectin, epinephrine, and rosiglitazone also control the expression of PDK4 in tissue-specific manners. In this review, we discuss several factors involved in the expressional regulation of PDK2 and PDK4, and introduce current studies aimed at providing a better understanding of the molecular mechanisms that underlie the development of metabolic diseases such as diabetes.

A metabolic prosurvival role for PML in breast cancer

Cancer cells exhibit an aberrant metabolism that facilitates more efficient production of biomass and hence tumor growth and progression. However, the genetic cues modulating this metabolic switch remain largely undetermined. We identified a metabolic function for the promyelocytic leukemia (PML) gene, uncovering an unexpected role for this bona fide tumor suppressor in breast cancer cell survival. We found that PML acted as both a negative regulator of PPARγ coactivator 1A (PGC1A) acetylation and a potent activator of PPAR signaling and fatty acid oxidation. We further showed that PML promoted ATP production and inhibited anoikis. Importantly, PML expression allowed luminal filling in 3D basement membrane breast culture models, an effect that was reverted by the pharmacological inhibition of fatty acid oxidation. Additionally, immunohistochemical analysis of breast cancer biopsies revealed that PML was overexpressed in a subset of breast cancers and enriched in triple-negative cases. Indeed, PML expression in breast cancer correlated strikingly with reduced time to recurrence, a gene signature of poor prognosis, and activated PPAR signaling. These findings have important therapeutic implications, as PML and its key role in fatty acid oxidation metabolism are amenable to pharmacological suppression, a potential future mode of cancer prevention and treatment.

Genome-wide profiling of peroxisome proliferator-activated receptor γ in primary epididymal, inguinal, and brown adipocytes reveals depot-selective binding correlated with gene expression

Peroxisome proliferator-activated receptor γ (PPARγ) is a master regulator of adipocyte differentiation and function. We and others have previously mapped PPARγ binding at a genome-wide level in murine and human adipocyte cell lines and in primary human adipocytes. However, little is known about how binding patterns of PPARγ differ between brown and white adipocytes and among different types of white adipocytes. Here we have employed chromatin immunoprecipitation combined with deep sequencing to map and compare PPARγ binding in in vitro differentiated primary mouse adipocytes isolated from epididymal, inguinal, and brown adipose tissues. While these PPARγ binding profiles are overall similar, there are clear depot-selective binding sites. Most PPARγ binding sites previously mapped in 3T3-L1 adipocytes can also be detected in primary adipocytes, but there are a large number of PPARγ binding sites that are specific to the primary cells, and these tend to be located in closed chromatin regions in 3T3-L1 adipocytes. The depot-selective binding of PPARγ is associated with highly depot-specific gene expression. This indicates that PPARγ plays a role in the induction of genes characteristic of different adipocyte lineages and that preadipocytes from different depots are differentially preprogrammed to permit PPARγ lineage-specific recruitment even when differentiated in vitro.