Plakoglobin regulates adipocyte differentiation independently of the Wnt/β-catenin signaling pathway

The scaffold protein 14-3-3ζ is an established regulator of adipogenesis and postnatal adiposity. We and others have demonstrated the 14-3-3ζ interactome to be diverse and dynamic, and it can be examined to identify novel regulators of physiological processes, including adipogenesis. In the present study, we sought to determine if factors that influence adipogenesis during the development of obesity could be identified in the 14-3-3ζ interactome found in white adipose tissue of lean or obese TAP-tagged-14-3-3ζ overexpressing mice. Using mass spectrometry, differences in the abundance of novel, as well as established, adipogenic factors within the 14-3-3ζ interactome could be detected in adipose tissues. One novel candidate was revealed to be plakoglobin, the homolog of the known adipogenic inhibitor, β-catenin, and herein, we report that plakoglobin is involved in adipocyte differentiation. Plakoglobin is expressed in murine 3T3-L1 cells and is primarily localized to the nucleus, where its abundance decreases during adipogenesis. Depletion of plakoglobin by siRNA inhibited adipogenesis and reduced PPARγ2 expression, and similarly, plakoglobin depletion in human adipose-derived stem cells also impaired adipogenesis and reduced lipid accumulation post-differentiation. Transcriptional assays indicated that plakoglobin does not participate in Wnt/β-catenin signaling, as its depletion did not affect Wnt3a-mediated transcriptional activity. Taken together, our results establish plakoglobin as a novel regulator of adipogenesis in vitro and highlights the ability of using the 14-3-3ζ interactome to identify potential pro-obesogenic factors.

PFO5DoDA disrupts hepatic homeostasis primarily through glucocorticoid signaling inhibition

Legacy per- and polyfluoroalkyl substances (PFASs) are a worldwide health concern due to their potential bioaccumulation and toxicity in humans. A variety of perfluoroether carboxylic acids (PFECAs) have been developed as next-generation replacements of legacy PFASs. However, information regarding their possible environmental and human health risks is limited. In the present study, we explored the effects of PFECAs on mice based on long-term exposure to environmentally relevant doses of perfluoro-3,5,7,9,11-pentaoxadodecanoic acid (PFO5DoDA). Results showed that PFECAs exposure suppressed many cellular stress signals and resulted in hepatomegaly. PFO5DoDA acted as an agonist of the peroxisome proliferator-activated receptor (PPAR) in vitro and modulated PPAR-dependent gene expression in the liver. Importantly, PFECAs had an inhibitory effect on the glucocorticoid receptor (GR), which may contribute to the extensive suppression of stress signals. Of note, the GR suppression induced by PFECAs was not reported by legacy perfluorooctanoic acid (PFOA). PFO5DoDA-induced changes in both GR and PPAR signals remodeled hepatic metabolic profiles, including decreased fatty acids and amino acids and increased β-oxidation. Mechanistically, PFO5DoDA inhibited GR transactivation by degradation of GR proteins. Our results emphasize the potential risk of PFECAs to human health, which were introduced to ease concerns regarding legacy PFASs.

Biochemical and structural basis for the pharmacological inhibition of nuclear hormone receptor PPARγ by inverse agonists

Recent studies have reported that the peroxisome proliferator–activated receptor gamma (PPARγ) pathway is activated in approximately 40% of patients with muscle-invasive bladder cancer. This led us to investigate pharmacological repression of PPARγ as a possible intervention strategy. Here, we characterize PPARγ antagonists and inverse agonists and find that the former behave as silent ligands, whereas inverse agonists (T0070907 and SR10221) repress downstream PPARγ target genes leading to growth inhibition in bladder cancer cell lines. To understand the mechanism, we determined the ternary crystal structure of PPARγ bound to T0070907 and the corepressor (co-R) peptide NCOR1. The structure shows that the AF-2 helix 12 (H12) rearranges to bind inside the ligand-binding domain, where it forms stabilizing interactions with the compound. This dramatic movement in H12 unveils a large interface for co-R binding. In contrast, the crystal structure of PPARγ bound to a SR10221 analog shows more subtle structural differences, where the compound binds and pushes H12 away from the ligand-binding domain to allow co-R binding. Interestingly, we found that both classes of compound promote recruitment of co-R proteins in biochemical assays but with distinct conformational changes in H12. We validate our structural models using both site-directed mutagenesis and chemical probes. Our findings offer new mechanistic insights into pharmacological modulation of PPARγ signaling.

Retinoid X Receptor: Cellular and Biochemical Roles of Nuclear Receptor with a Focus on Neuropathological Involvement

Retinoid X receptors (RXRs) present a subgroup of the nuclear receptor superfamily with particularly high evolutionary conservation of ligand binding domain. The receptor exists in α, β, and γ isotypes that form homo-/heterodimeric complexes with other permissive and non-permissive receptors. While research has identified the biochemical roles of several nuclear receptor family members, the roles of RXRs in various neurological disorders remain relatively under-investigated. RXR acts as ligand-regulated transcription factor, modulating the expression of genes that plays a critical role in mediating several developmental, metabolic, and biochemical processes. Cumulative evidence indicates that abnormal RXR signalling affects neuronal stress and neuroinflammatory networks in several neuropathological conditions. Protective effects of targeting RXRs through pharmacological ligands have been established in various cell and animal models of neuronal injury including Alzheimer disease, Parkinson disease, glaucoma, multiple sclerosis, and stroke. This review summarises the existing knowledge about the roles of RXR, its interacting partners, and ligands in CNS disorders. Future research will determine the importance of structural and functional heterogeneity amongst various RXR isotypes as well as elucidate functional links between RXR homo- or heterodimers and specific physiological conditions to increase drug targeting efficiency in pathological conditions.

Peroxisome Proliferator-Activated Receptors (PPAR), fatty acids and microRNAs: Implications in women delivering low birth weight babies

Low birth weight (LBW) babies are associated with neonatal morbidity and mortality and are at increased risk for noncommunicable diseases (NCDs) in later life. However, the molecular determinants of LBW are not well understood. Placental insufficiency/dysfunction is the most frequent etiology for fetal growth restriction resulting in LBW and placental epigenetic processes are suggested to be important regulators of pregnancy outcome. Early life exposures like altered maternal nutrition may have long-lasting effects on the health of the offspring via epigenetic mechanisms like DNA methylation and microRNA (miRNA) regulation. miRNAs have been recognized as major regulators of gene expression and are known to play an important role in placental development. Angiogenesis in the placenta is known to be regulated by transcription factor peroxisome proliferator-activated receptor (PPAR) which is activated by ligands such as long-chain-polyunsaturated fatty acids (LCPUFA). In vitro studies in different cell types indicate that fatty acids can influence epigenetic mechanisms like miRNA regulation. We hypothesize that maternal fatty acid status may influence the miRNA regulation of PPAR genes in the placenta in women delivering LBW babies. This review provides an overview of miRNAs and their regulation of PPAR gene in the placenta of women delivering LBW babies.Abbreviations: AA - Arachidonic Acid; Ago2 - Argonaute2; ALA - Alpha-Linolenic Acid; ANGPTL4 - Angiopoietin-Like Protein 4; C14MC - Chromosome 14 miRNA Cluster; C19MC - Chromosome 19 miRNA Cluster; CLA - Conjugated Linoleic Acid; CSE - Cystathionine γ-Lyase; DHA - Docosahexaenoic Acid; EFA - Essential Fatty Acids; E2F3 - E2F transcription factor 3; EPA - Eicosapentaenoic Acid; FGFR1 - Fibroblast Growth Factor Receptor 1; GDM - Gestational Diabetes Mellitus; hADMSCs - Human Adipose Tissue-Derived Mesenchymal Stem Cells; hBMSCs - Human Bone Marrow Mesenchymal Stem Cells; HBV - Hepatitis B Virus; HCC - Hepatocellular Carcinoma; HCPT - Hydroxycamptothecin; HFD - High-Fat Diet; Hmads - Human Multipotent Adipose-Derived Stem; HSCS - Human Hepatic Stellate Cells; IUGR - Intrauterine Growth Restriction; LA - Linoleic Acid; LBW - Low Birth Weight; LCPUFA - Long-Chain Polyunsaturated Fatty Acids; MEK1 - Mitogen-Activated Protein Kinase 1; MiRNA - MicroRNA; mTOR - Mammalian Target of Rapamycin; NCDs - NonCommunicable Diseases; OA - Oleic Acid; PASMC - Pulmonary Artery Smooth Muscle Cell; PLAG1 - Pleiomorphic Adenoma Gene 1; PPAR - Peroxisome Proliferator-Activated Receptor; PPARα - PPAR alpha; PPARγ - PPAR gamma; PPARδ - PPAR delta; pre-miRNA - precursor miRNA; RISC - RNA-Induced Silencing Complex; ROS - Reactive Oxygen Species; SAT - Subcutaneous Adipose Tissue; WHO - World Health Organization.

Human hepatic in vitro models reveal distinct anti-NASH potencies of PPAR agonists

Non-alcoholic steatohepatitis (NASH) is a highly prevalent, chronic liver disease characterized by hepatic lipid accumulation, inflammation, and concomitant fibrosis. Up to date, no anti-NASH drugs have been approved. In this study, we reproduced key NASH characteristics in vitro by exposing primary human hepatocytes (PHH), human skin stem cell-derived hepatic cells (hSKP-HPC), HepaRG and HepG2 cell lines, as well as LX-2 cells to multiple factors that play a role in the onset of NASH. The obtained in vitro disease models showed intracellular lipid accumulation, secretion of inflammatory chemokines, induced ATP content, apoptosis, and increased pro-fibrotic gene expression. These cell systems were then used to evaluate the anti-NASH properties of eight peroxisome proliferator-activated receptor (PPAR) agonists (bezafibrate, elafibranor, fenofibrate, lanifibranor, pemafibrate, pioglitazone, rosiglitazone, and saroglitazar). PPAR agonists differently attenuated lipid accumulation, inflammatory chemokine secretion, and pro-fibrotic gene expression.Based on the obtained readouts, a scoring system was developed to grade the anti-NASH potencies. The in vitro scoring system, based on a battery of the most performant models, namely PHH, hSKP-HPC, and LX-2 cultures, showed that elafibranor, followed by saroglitazar and pioglitazone, induced the strongest anti-NASH effects. These data corroborate available clinical data and show the relevance of these in vitro models for the preclinical investigation of anti-NASH compounds.

Cannabidiol and Cannabinoid Compounds as Potential Strategies for Treating Parkinson's Disease and L-DOPA-Induced Dyskinesia

Parkinson's disease (PD) and L-DOPA-induced dyskinesia (LID) are motor disorders with significant impact on the patient's quality of life. Unfortunately, pharmacological treatments that improve these disorders without causing severe side effects are not yet available. Delay in initiating L-DOPA is no longer recommended as LID development is a function of disease duration rather than cumulative L-DOPA exposure. Manipulation of the endocannabinoid system could be a promising therapy to control PD and LID symptoms. In this way, phytocannabinoids and synthetic cannabinoids, such as cannabidiol (CBD), the principal non-psychotomimetic constituent of the Cannabis sativa plant, have received considerable attention in the last decade. In this review, we present clinical and preclinical evidence suggesting CBD and other cannabinoids have therapeutic effects in PD and LID. Here, we discuss CBD pharmacology, as well as its neuroprotective effects and those of other cannabinoids. Finally, we discuss the modulation of several pro- or anti-inflammatory factors as possible mechanisms responsible for the therapeutic/neuroprotective potential of Cannabis-derived/cannabinoid synthetic compounds in motor disorders.

Upregulated PDK4 expression is a sensitive marker of increased fatty acid oxidation

Fatty acid oxidation is a central fueling pathway for mitochondrial ATP production. Regulation occurs through multiple nutrient- and energy-sensitive molecular mechanisms. We explored if upregulated mRNA expression of the mitochondrial enzyme pyruvate dehydrogenase kinase 4 (PDK4) may be used as a surrogate marker of increased mitochondrial fatty acid oxidation, by indicating an overall shift from glucose to fatty acids as the preferred oxidation fuel. The association between fatty acid oxidation and PDK4 expression was studied in different contexts of metabolic adaption. In rats treated with the modified fatty acid tetradecylthioacetic acid (TTA), Pdk4 was upregulated simultaneously with fatty acid oxidation genes in liver and heart, whereas muscle and white adipose tissue remained unaffected. In MDA-MB-231 cells, fatty acid oxidation increased nearly three-fold upon peroxisome proliferator-activated receptor α (PPARα, PPARA) overexpression, and four-fold upon TTA-treatment. PDK4 expression was highly increased under these conditions. Further, overexpression of PDK4 caused increased fatty acid oxidation in these cells. Pharmacological activators of PPARα and AMPK had minor effects, while the mTOR inhibitor rapamycin potentiated the effect of TTA. There were minor changes in mitochondrial respiration, glycolytic function, and mitochondrial biogenesis under conditions of increased fatty acid oxidation. TTA was found to act as a mild uncoupler, which is likely to contribute to the metabolic effects. Repeated experiments with HeLa cells supported these findings. In summary, PDK4 upregulation implies an overarching metabolic shift towards increased utilization of fatty acids as energy fuel, and thus constitutes a sensitive marker of enhanced fatty acid oxidation.

Genetic polymorphisms of PPAR genes and human cancers: evidence for gene-environment interactions

Peroxisome proliferator-activated receptors (PPARs) are nuclear transcription factors that play a role in lipid metabolism, cell proliferation, terminal differentiation, apoptosis, and inflammation. Although several cancer models have been suggested to explain PPARs' involvement in tumorigenesis, however, their role is still unclear. In this review, we examined associations of the different PPARs, polymorphisms and various types of cancer with a focus on gene-environment interactions. Reviewed evidence suggests that functional genetic variants of the different PPARs may modulate the relationship between environmental exposure and cancer risk. In addition, this report unveils the scarcity of reliable quantitative environmental exposure data when examining these interactions, and the current gaps in studying gene-environment interactions in many types of cancer, particularly colorectal, prostate, and bladder cancers.

Analysis of the PPARD Gene Expression Level Changes in Football Players in Response to the Training Cycle

The PPARD gene codes protein that belongs to the peroxisome proliferator-activated receptor (PPAR) family engaged in a variety of biological processes, including lipid metabolism in muscle cells. In this study, we assess the relationship between PPARD gene expression lipid metabolism parameters and the variation of the PPARD gene expression before (T₁) and after 12 hours of training (T₂) sessions in a group of football players. Peripheral blood lymphocytes were obtained from 22 football players (17.5±0.7 years, 178±0.7 cm, 68.05±9.18 kg). The PPARD gene expression, analyzed by quantitative polymerase chain reaction (qPCR), was significantly higher after T₂ (p = 0.0006). Moreover, at the end of the training cycle, there was a significant decrease in relative fat tissue (FAT) (%) (p = 0.01) and absolute FAT (kg) (p = 0.01). A negative correlation was observed between absolute FAT (kg) and PPARD gene expression level in T₂ (p = 0.03). The levels of cholesterol and triglyceride (TG) fractions were not significantly different (p >0.05) before and after training. No significant relationship between PPARD expression and cholesterol or TG levels was found. We found that physical training affects PPARD expression. Moreover, the negative correlation between PPARD expression and absolute FAT (kg) level may be indicative of the contribution of PPARD in metabolic adaptation to increased lipid uptake that can be used to control the body composition of athletes.

Circadian Rhythms in Diet-Induced Obesity

The biological clocks of the circadian timing system coordinate cellular and physiological processes and synchronizes these with daily cycles, feeding patterns also regulates circadian clocks. The clock genes and adipocytokines show circadian rhythmicity. Dysfunction of these genes are involved in the alteration of these adipokines during the development of obesity. Food availability promotes the stimuli associated with food intake which is a circadian oscillator outside of the suprachiasmatic nucleus (SCN). Its circadian rhythm is arranged with the predictable daily mealtimes. Food anticipatory activity is mediated by a self-sustained circadian timing and its principal component is food entrained oscillator. However, the hypothalamus has a crucial role in the regulation of energy balance rather than food intake. Fatty acids or their metabolites can modulate neuronal activity by brain nutrient-sensing neurons involved in the regulation of energy and glucose homeostasis. The timing of three-meal schedules indicates close association with the plasma levels of insulin and preceding food availability. Desynchronization between the central and peripheral clocks by altered timing of food intake and diet composition can lead to uncoupling of peripheral clocks from the central pacemaker and to the development of metabolic disorders. Metabolic dysfunction is associated with circadian disturbances at both central and peripheral levels and, eventual disruption of circadian clock functioning can lead to obesity. While CLOCK expression levels are increased with high fat diet-induced obesity, peroxisome proliferator-activated receptor (PPAR) alpha increases the transcriptional level of brain and muscle ARNT-like 1 (BMAL1) in obese subjects. Consequently, disruption of clock genes results in dyslipidemia, insulin resistance and obesity. Modifying the time of feeding alone can greatly affect body weight. Changes in the circadian clock are associated with temporal alterations in feeding behavior and increased weight gain. Thus, shift work is associated with increased risk for obesity, diabetes and cardio-vascular diseases as a result of unusual eating time and disruption of circadian rhythm.

Characterisation of peroxisome proliferator-activated receptor signalling in the midbrain periaqueductal grey of rats genetically prone to heightened stress, negative affect and hyperalgesia

The stress-hyperresponsive Wistar-Kyoto (WKY) rat strain exhibits a hyperalgesic phenotype and is a useful genetic model for studying stress-pain interactions. Peroxisome proliferator-activated receptor (PPAR) signalling in the midbrain periaqueductal grey (PAG) modulates pain. This study characterised PPAR signalling in the PAG of WKY rats exposed to the formalin test of inflammatory pain, versus Sprague-Dawley (SD) controls. Formalin injection reduced levels of the endogenous PPAR ligands N-palmitoylethanolamide (PEA) and N-oleoylethanolamide (OEA) in the lateral(l) PAG of SD rats, but not WKY rats which exhibited higher levels of these analytes compared with formalin-injected SD counterparts. Levels of mRNA coding for fatty acid amide hydrolase (FAAH; catabolises PEA and OEA) were lower in the lPAG of WKY versus SD rats. PPARγ mRNA and protein levels in the lPAG were higher in saline-treated WKY rats, with PPARγ protein levels reduced by formalin treatment in WKY rats only. In the dorsolateral(dl) or ventrolateral(vl) PAG, there were no effects of formalin injection on PEA or OEA levels but there were some differences in levels of these analytes between saline-treated WKY and SD rats and some formalin-evoked alterations in levels of PPARα, PPARγ or FAAH mRNA in WKY and/or SD rats. Pharmacological blockade of PPARγ in the lPAG enhanced formalin-evoked nociceptive behaviour in WKY, but not SD, rats. These data indicate differences in the PPAR signalling system in the PAG of WKY versus SD rats and suggest that enhanced PEA/OEA-mediated tone at PPARγ in the lPAG may represent an adaptive mechanism to lower hyperalgesia in WKY rats.

Prenatal fat exposure and hypothalamic PPAR β/δ: Possible relationship to increased neurogenesis of orexigenic peptide neurons

Gestational exposure to a fat-rich diet, while elevating maternal circulating fatty acids, increases in the offspring's hypothalamus and amygdala the proliferation and density of neurons that express neuropeptides known to stimulate consummatory behavior. To understand the relationship between these phenomena, this study examined in the brain of postnatal offspring (day 15) the effect of prenatal fat exposure on the transcription factor, peroxisome proliferator-activated receptor (PPAR) β/δ, which is sensitive to fatty acids, and the relationship of PPAR β/δ to the orexigenic neuropeptides, orexin, melanin-concentrating hormone, and enkephalin. Prenatal exposure to a fat-rich diet compared to low-fat chow increased the density of cells immunoreactive for PPAR β/δ in the hypothalamic paraventricular nucleus (PVN), perifornical lateral hypothalamus (PFLH), and central nucleus of the amygdala (CeA), but not the hypothalamic arcuate nucleus or basolateral amygdaloid nucleus. It also increased co-labeling of PPAR β/δ with the cell proliferation marker, BrdU, or neuronal marker, NeuN, and the triple labeling of PPAR β/δ with BrdU plus NeuN, indicating an increase in proliferation and density of new PPAR β/δ neurons. Prenatal fat exposure stimulated the double-labeling of PPAR β/δ with orexin or melanin-concentrating hormone in the PFLH and enkephalin in the PVN and CeA and also triple-labeling of PPAR β/δ with BrdU and these neuropeptides, indicating that dietary fat increases the genesis of PPAR β/δ neurons that produce these peptides. These findings demonstrate a close anatomical relationship between PPAR β/δ and the increased proliferation and density of peptide-expressing neurons in the hypothalamus and amygdala of fat-exposed offspring.

Isomeric effects of anti-diabetic α-lipoic acid with γ-cyclodextrin

AIMS

Previous studies reported the anti-diabetic effects of α-lipoic acid (αLA) isomers: racemic-αLA, R-αLA, or S-αLA. Previously, we examined the anti-diabetic effects of αLA administered as a food additive, but were unable to demonstrate the differences among different isomers. In this study, αLAs were complexed with γ-cyclodextrin (γCD) for the stability.We then investigated the anti-diabetic effects of racemic-, R-, and S-αLA/γCDs in KKAy mice.

MAIN METHODS

Male type 2 diabetic KKAy mice were divided into 5 groups, and fed either a high-fat-diet (HFD),HFD supplemented with γCD, or HFD supplemented with racemic-αLA/γCD, R-αLA/γCD, or S-αLA/γCD for 4 weeks. At the end of the feeding period, HbA1c and adiponectin levels were measured, PPARγ2mRNA expression levels were assessed in adipose tissues using real-time PCR, and AMP-activated protein kinase (AMPK) phosphorylation levels were evaluated in the liver by Western blotting.

KEY FINDINGS

The anti-diabetic effects of αLA; the isomeric compounds racemic-, R-, and S-αLA/γCD were investigated using amale type 2 diabetic KKAy mousemodel. Significant differences were observed in HbA1c and plasma adiponectin levels between R-αLA/γCD-treated mice and control mice. PPARγ2 mRNA expression levels were slightly higher in racemic- and R-αLA/γCD-treated mice. Moreover, AMPK phosphorylation levels were elevated in racemic-αLA/γCD- and R-αLA/γCD-treated mice, but remained unchanged in S-αLA/γCD-treated mice.

SIGNIFICANCE

These results suggested that the stereoisomerism mediates a difference in the anti-diabetic effects of racemic-, R-, and S-αLA/γCDs. Furthermore, the anti-diabetic mechanism of αLA/γCD action may be attributed to the activation of AMPK in the liver.