ABSTRACT
The nuclear receptor constitutive androstane receptor (CAR) (NR1I3) regulates hepatic genes involved in xenobiotic detoxification as well as genes involved in energy homeostasis. We provide data that extend the role of CAR to regulation of serum triglyceride levels under conditions of metabolic/nutritional stress. The typically high serum triglyceride levels of ob/ob mice were completely normalized when crossed onto a Car(-/-) (mice deficient for the Car gene) genetic background. Moreover, increases in serum triglycerides observed after a high-fat diet (HFD) regime were not observed in Car(-/-) animals. Conversely, pharmacological induction of CAR activity using the selective mouse CAR agonist TCPOBOP during HFD feeding resulted in a CAR-dependent increase in serum triglyceride levels. A major regulator of hepatic fatty oxidation is the nuclear receptor PPARalpha (NR1C1). The expression of peroxisome proliferator-activated receptor alpha (PPARalpha) target genes was inversely related to the activity of CAR. Consistent with these observations, Car(-/-) animals exhibited increased hepatic fatty acid oxidation. Treatment of mice with 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) significantly decreased expression of PPARalpha mRNA as well as Cyp4a14, CPT1alpha, and cytosolic Acyl-CoA thioesterase (CTE) in the liver. These data have implications in disease therapy such as for diabetes and nonalcoholic steatohepatitis (NASH).
Subject(s)
Receptors, Cytoplasmic and Nuclear/metabolism , Transcription Factors/metabolism , Triglycerides/blood , Animals , Base Sequence , Constitutive Androstane Receptor , DNA Primers/genetics , Dietary Fats/administration & dosage , Fatty Acids/metabolism , Lipid Metabolism , Liver/drug effects , Liver/metabolism , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Mice, Obese , Oligonucleotide Array Sequence Analysis , PPAR alpha/genetics , PPAR alpha/metabolism , Pyridines/pharmacology , RNA, Messenger/genetics , RNA, Messenger/metabolism , Receptors, Cytoplasmic and Nuclear/agonists , Receptors, Cytoplasmic and Nuclear/deficiency , Receptors, Cytoplasmic and Nuclear/genetics , Stress, Physiological , Transcription Factors/agonists , Transcription Factors/deficiency , Transcription Factors/geneticsABSTRACT
The identification of small molecule ligands for the peroxisome proliferator-activated receptors (PPARs) has been instrumental in elucidating their biological roles. In particular, agonists have been the focus of much of the research in the field with relatively few antagonists being described and all of those being selective for PPARalpha or PPARgamma. The comparison of these agonist and antagonist ligands in cellular and animal systems has often led to surprising results and new insights into the biology of the PPARs. The PPARbeta/delta receptor is emerging as an important regulator of energy metabolism, inflammation, and cell growth and differentiation; however, only agonist ligands have been described for this receptor thus far. Here we describe the first report of a PPARbeta/delta small molecule antagonist ligand. This antagonist ligand will be a useful tool for elucidating the biological roles of PPARbeta/delta.
Subject(s)
Ligands , PPAR delta/antagonists & inhibitors , PPAR-beta/antagonists & inhibitors , Cells, Cultured , Chromatin Immunoprecipitation , Dose-Response Relationship, Drug , Fatty Acids/metabolism , Fluorescence Resonance Energy Transfer , Gene Expression Regulation/drug effects , Humans , Molecular Structure , Muscle, Skeletal/cytology , Muscle, Skeletal/drug effects , Muscle, Skeletal/metabolism , Oxidation-Reduction/drug effects , Sulfones/chemistry , Sulfones/pharmacology , Thiazoles/chemistry , Thiazoles/pharmacology , Thiophenes/chemistry , Thiophenes/pharmacologyABSTRACT
OBJECTIVE: Exercise increases fatty acid oxidation (FAO), improves serum high density lipoprotein cholesterol (HDLc) and triglycerides (TG), and upregulates skeletal muscle peroxisome proliferator activated receptor (PPAR)delta expression. In parallel, PPARdelta agonist-upregulated FAO would induce fatty-acid uptake (via peripheral lipolysis), and influence HDLc and TG-rich lipoprotein particle metabolism, as suggested in preclinical models. METHODS AND RESULTS: Healthy volunteers were allocated placebo (n=6) or PPARdelta agonist (GW501516) at 2.5 mg (n=9) or 10 mg (n=9), orally, once-daily for 2 weeks while hospitalized and sedentary. Standard lipid/lipoproteins were measured and in vivo fat feeding studies were conducted. Human skeletal muscle cells were treated with GW501516 in vitro and evaluated for lipid-related gene expression and FAO. Serum TG trended downwards (P=0.08, 10 mg), whereas TG clearance post fat-feeding improved with drug (P=0.02). HDLc was enhanced in both treatment groups (2.5 mg P=0.004, 10 mg P<0.001) when compared with the decrease in the placebo group (-11.5+/-1.6%, P=0.002). These findings complimented in vitro cell culture results whereby GW501516 induced FAO and upregulated CPT1 and CD36 expression, in addition to a 2-fold increase in ABCA1 (P=0.002). However, LpL expression remained unchanged. CONCLUSIONS: This is the first report of a PPARdelta agonist administered to man. In this small study, GW501516 significantly influenced HDLc and TGs in healthy volunteers. Enhanced in vivo serum fat clearance, and the first demonstrated in vitro upregulation in human skeletal muscle fat utilization and ABCA1 expression, suggests peripheral fat utilization and lipidation as potential mechanisms toward these HDL:TG effects.
Subject(s)
Lipoproteins, HDL/metabolism , PPAR delta/agonists , Thiazoles/pharmacology , Triglycerides/metabolism , ATP Binding Cassette Transporter 1 , ATP-Binding Cassette Transporters/genetics , ATP-Binding Cassette Transporters/metabolism , Adult , CD36 Antigens/genetics , CD36 Antigens/metabolism , Cells, Cultured , Fatty Acids/metabolism , Humans , Male , Muscle, Skeletal/cytology , Muscle, Skeletal/drug effects , Muscle, Skeletal/metabolism , Oxidation-Reduction/drug effects , PPAR delta/genetics , PPAR delta/metabolism , Up-Regulation/drug effectsABSTRACT
Peptide antagonists of the human papillomavirus type 11 (HPV-11) E2-DNA association were identified using a filamentous bacteriophage random peptide library. Synthetic peptides antagonized the E2-DNA interaction, effectively blocked E2-mediated transcriptional activation of a reporter gene in cell culture, and inhibited E1-E2-mediated HPV-11 DNA replication in vitro. These peptides may prove to be useful tools for characterizing E2 function and for exploring the effectiveness of E2-inhibitor-based treatments for HPV-associated diseases.
