Adipocyte-Derived PXR Signaling Is Dispensable for Diet-Induced Obesity and Metabolic Disorders in Mice.

PXR interaction with p53: a meeting of two masters

OF DISSERTATION THE ROLE OF PXR AND IKKβ SIGNALING IN CARDIOMETABOLIC DISEASE Cardiovascular disease (CVD) is the leading cause of death worldwide and is partially attributed to perturbations in lipid metabolism. Xenobiotics, such as pharmaceutical drugs and environmental chemicals, have been associated with increased risk of CVD in multiple large-scale human population studies, but the underlying mechanisms remain poorly defined. We and others have identified several xenobiotics as potent agonists for the pregnane X receptor (PXR), a nuclear receptor that can be activated by numerous drugs as well as environmental and dietary chemicals. However, the role of PXR in mediating the pathophysiological effects of xenobiotic exposure in humans and animals remains elusive. The work herein identified several widely used pharmaceutical agents and endocrine disrupting chemicals as PXR-selective agonists such as drugs involved in HIV therapy and phthalates/phthalate substitutes, respectively. We investigated the role of amprenavir, an HIV protease inhibitor, and tributyl citrate, a phthalate substitute, on PXR-dependent alterations in lipoprotein metabolism. Acute exposure with either xenobiotic in mice elicited increases in the proatherogenic LDL-cholesterol levels in a PXR-dependent manner. PXR activation significantly induced expression of genes involved in intestinal lipid metabolism. Further, we went on to identify the intestinal cholesterol transporter, Niemann-Pick C1-Like 1 (NPC1L1), as a direct PXR-target gene. PXR activation also stimulated cholesterol uptake in both murine and human intestinal cells. Moreover, we provide evidence that the microsomal triglyceride transfer protein (MTP) may be a direct PXR-target gene. Taken together, these findings provide critical mechanistic insight into the role of xenobiotic-mediated PXR activation on lipid homeostasis and demonstrate a potential role of PXR in mediating adverse effects of xenobiotics on CVD risk in humans. In addition to PXR signaling, we investigated the role of IκB kinase β (IKKβ), a central coordinator of inflammation, in adipocyte progenitor cells. Targeting IKKβ in adipose progenitor cells resulted in decreased high fat diet (HFD)-elicited adipogenesis, while protecting mice from inflammation and associated insulin resistance. Consistently, we discovered that IKKβ inhibition by antisense oligonucleotides ablated HFD-induced adiposity, while protecting mice against associated metabolic disorders. In conclusion, targeting IKKβ with antisense therapy may present as a novel therapeutic approach to combat obesity and metabolic dysfunctions.

RNA-Seq reveals common and unique PXR- and CAR-target gene signatures in the mouse liver transcriptome

The pregnane X receptor (PXR) is a nuclear receptor that can be activated by numerous drugs and xenobiotic chemicals. PXR thereby functions as a xenobiotic sensor to coordinately regulate host responses to xenobiotics by transcriptionally regulating many genes involved in xenobiotic metabolism. We have previously reported that PXR has pro-atherogenic effects in animal models, but how PXR contributes to atherosclerosis development in different tissues or cell types remains elusive. In this study, we generated an LDL receptor-deficient mouse model with myeloid-specific PXR deficiency (PXRΔMyeLDLR-/-) to elucidate the role of macrophage PXR signaling in atherogenesis. The myeloid PXR deficiency did not affect metabolic phenotypes and plasma lipid profiles, but PXRΔMyeLDLR-/- mice had significantly decreased atherosclerosis at both aortic root and brachiocephalic arteries compared with control littermates. Interestingly, the PXR deletion did not affect macrophage adhesion and migration properties, but reduced lipid accumulation and foam cell formation in the macrophages. PXR deficiency also led to decreased expression of the scavenger receptor CD36 and impaired lipid uptake in macrophages of the PXRΔMyeLDLR-/- mice. Further, RNA-Seq analysis indicated that treatment with a prototypical PXR ligand affects the expression of many atherosclerosis-related genes in macrophages in vitro. These findings reveal a pivotal role of myeloid PXR signaling in atherosclerosis development and suggest that PXR may be a potential therapeutic target in atherosclerosis management.

Hepatic Fatty Acid Transporter Cd36 Is a Common Target of LXR, PXR, and PPARγ in Promoting Steatosis

Non-nucleoside reverse transcriptase inhibitor efavirenz activates PXR to induce hypercholesterolemia and hepatic steatosis

Background: Stevioside is used as a sweetener in food additives and pharmaceutical products. There is a growing concern about the adverse effects posed by stevioside usage. Stevioside is hydrolyzed into the aglycone steviol that is absorbed into the body. Recent studies suggest that steviol, but not stevioside, activates Pregnane X receptor (PXR) in human hepatic cells. In addition to the role in xenobiotic metabolism, the atherogenic and dyslipidemic effects of PXR have been revealed. Controversially, steviol not only increases the mRNA expression of PXR direct downstream gene CYP3A4, but also inhibits the enzymatic activities of CYP3A4. Thus, it is urgent to elucidate the molecular mechanisms by which steviol activates PXR signaling and to assess the possible adverse effects of steviol on pro-atherosclerotic events, such as dyslipidemia. Objective: Our study aims to explore the molecular mechanisms by which exposure to steviol activates human PXR and increases the risk of dyslipidemia. Methods: Both human hepatic and intestinal cells were used to test if steviol was a PXR agonist via transfection assay. The key residues within PXR’s ligand-binding pocket that steviol interacted with were investigated using a computational docking study with site-directed mutagenesis assay. Human intestinal cells were treated with steviol and/or PXR antagonist resveratrol (RES) to estimate the function of steviol in cholesterol uptake. Individual pairwise comparisons and other comparisons were analyzed with Student’s t-test and two-way ANOVA, respectively. Results: Steviol was a more potent agonist of human PXR than mouse PXR. Steviol promoted PXR to dissociate from its nuclear co-repressors. The key amino acids that were essential for the agonistic effects of steviol within PXR’s ligand binding pocket were established. Mechanistically, steviol induced gene expression of key intestinal cholesterol transporters, which led to increased cholesterol uptake by intestinal cells. Future studies in mice are needed to explore if exposure to steviol alters in vivo lipid profiles via PXR signaling. Our study provides potential evidence for the future risk assessment of steviol on cardiovascular disease. Keywords: Steviol, PXR, cholesterol uptake, dyslipidemia

Cardiovascular disease is the leading cause of death. Many cardiovascular health problems, such as atherosclerosis, are caused by dyslipidemia. One xenobiotic nuclear receptor, Pregnane X Receptor (PXR), plays a significant role in atherosclerosis and dyslipidemia, and is activated by various environmental chemicals, including endocrine-disrupting chemicals (EDCs). EDCs are found in common household items such as plastics, medications, and food. Trazodone is a clinically used medication to treat depression by aiding in restoring the balance of serotonin in the brain. But it is unclear if Trazodone has possible impacts on cardiovascular risk factors such as dyslipidemia. Our preliminary data suggested that Trazodone activated human PXR in both intestinal (LS180) and hepatic (HepG2) cells. We hypothesize that Trazodone could regulate the cholesterol uptake mediated by PXR signaling. In this study we use cell-based transfection assay to evaluate the underlying mechanisms by which Trazodone activates PXR. We found that Trazodone was a more potent agonist of human PXR than mouse PXR. Trazodone could activate PXR more intensely in human liver cells compared with human intestinal cells. Our data suggested that Trazodone was a selective PXR agonist and promoted the dissociation between PXR and its nuclear corepressors. Next, we are to identify the key amino acid residues within PXR ligand binding pocket that interact with Trazodone by using computational docking study along with site-mutagenesis assay. Furthermore, we plan to estimate if Trazodone altered cholesterol uptake by human intestinal cells using fluorescence-labeled cholesterol. In conclusion, we explore the potential molecular mechanisms of how FDA-approved antidepressant Trazodone activates human PXR and increases the possible risk of dyslipidemia, which provides potential evidence on future cardiovascular disease risk assessment for Trazodone as well as other antidepressant drugs.

Reduced Nogo expression inhibits diet-induced metabolic disorders by regulating ChREBP and insulin activity

Preface. Abbreviations. Contributors. Chapter 1. Drug Metabolism: Significance and Challenges (Chandra Prakash and Alfin D.N. Vaz). 1.1. Introduction. 1.2. Phase I Drug Metabolizing Enzymes. 1.3. Phase II Conjugative Enzymes. 1.4. Drug Efflux Transporters. 1.5. Drug Uptake Transporters. 1.6. Challenges in Drug Metabolism. 1.7. Summary. 1.8. References. Chapter 2. Establishing Orphan Nuclear Receptors PXR and CAR as Xenobiotic Receptors (Tao Li, Junichiro Sonoda, and Ronald M. Evans). 2.1. Introduction. 2.2. Nuclear Receptor and Orphan Nuclear Receptor Superfamily. 2.3. Orphan Nuclear Receptors as Xenobiotic Receptors and Their Implications in Phase I Enzyme Regulation. 2.4. Perspectives. 2.5. References. Chapter 3. Nuclear Receptor-Mediated Regulation of Phase II Conjugating Enzymes (Olivier Barbier). 3.1. Introduction. 3.2. Phase II Drug Metabolizing Enzymes. 3.3. The Xenosensors CAR and PXR: 2 Masters Regulators of Phase II Metabolism. 3.4. AhR And Nrf2, Two Important Regulators of Phase II Enzymes. 3.5. PPARS and Phase II XMEs Regulation. 3.6. FXR/LXR and Phase II XMEs Regulation. 3.7. HNF and Phase II XMEs Regulation. 3.8. Regulation of Phase II Conjugating Enzymes by Steroid and Thyroid Receptors. 3.9. Concluding remarks and perspectives. 3.10. References. Chapter 4. Nuclear Receptor-Mediated Regulation of Drug Transporters (Oliver Burk). 4.1. Introduction. 4.2. Drug Transporters. 4.3. Induction of Drug Transporters by Activation of PXR and CAR. 4.4. Induction of Drug Transporters by Activation of PPARa. 4.5. Molecular Mechanism of PXR- and CAR-Dependent Drug Transporter Regulation. 4.6. Induction of Drug Transporter Expression and Drug Disposition. 4.7. Conclusions and Future Perspectives. 4.8. References. Chapter 5. Structure and Function of PXR and CAR (X. Edward Zhou and H. Eric Xu). 5.1. Introduction. 5.2. Structure and Function of PXR. 5.3. Structure and Function of CAR. 5.4. Concluding Remarks. 5.5. References. Chapter 6. Xenobiotic Receptor CoFactors and Coregulators (John Y. L. Chiang). 6.1. Regulation of PXR and CAR Nuclear Translocation. 6.2. Nuclear Receptor Coregulators and Epigenetic Regulation of Gene Transcription. 6.3. PXR and CAR Crosstalk with other Nuclear Receptors and Transcription Factors. 6.4. PXR and CAR Regulation of Lipid and Glucose Homeostasis. 6.5. Conclusion. 6.6. References. Chapter 7. Animal Models of Xenobiotic Nuclear Receptors and Their Utility in Drug Development (Haibiao Gong and Wen Xie). 7.1. Introduction. 7.2. PXR and CAR Loss-of-Function (Knock Out) Mouse Models. 7.3. PXR and CAR Gain-of-Function (Transgenic) Mouse Models. 7.4. Humanized Mouse Models. 7.5. Utility of Xenobiotic Mouse Models in Pharmaceutical Development. 7.6. Closing Remarks. 7.7. References. Chapter 8. Nuclear Receptors and Drug-Drug Interactions with Prescription Drugs and Herbal Medicines (Rommel G. Tirona and Richard B. Kim). 8.1. Introduction. 8.2. Prescription Drugs/Drug Classes Commonly Involved in Inductive Interactions. 8.3. Herbal Drug Medicines Commonly Involved in Inductive Interactions. 8.4. Pharmacology of Induction. 8.5. Clinical Aspects of Induction-Type Drug Interactions. 8.6. Inhibition of Nuclear Receptors in Clinical Drug Interactions. 8.7. Nuclear Receptor-Mediated Drug Side-Effects. 8.8. Perspectives. 8.9. References. Chapter 9. Genetic Variants of Xenobiotic Receptors and Their Implications in Drug Metabolism and Pharmacogenetics (Jatinder Lamba and Erin G. Schuetz). 9.1. PXR (Pregnane X Receptor) Background. 9.2. PXR Gene Structure. 9.3. PXR Alternative mRNAs. 9.4. Genetic Variants in PXR's Exons and their Functional Consequences. 9.5. Genetic Variants In Introns 2-8 and the 3'-UTR of PXR and their Functional Consequences. 9.6. Resequencing Strategy for the PXR Promoter and Intron 1. 9.7. Genetic Variation in the PXR Promoter and 5'-UTR and its Functional Relevance. 9.8. Genetic Variation in PXR's Intron 1 and its Functional Relevance. 9.9. In Silico Analysis for Functional Effect of SNPs in PXR's Promoter, 5'-UTR and Intron 1. 9.10. SNPs in PXR's Promoter and Intron 1 Affect Putative HNF Binding Sites. 9.11. PXR SNPs Have Been Associated with Intestinal and Hepatic Inflammation and Diseases. 9.12. PXR Structural Variation and other Genomic Features. 9.13. PXR Summary. 9.14. CAR-Background. 9.15. CAR Gene Structure. 9.16. CAR Alternatively Spliced RNAs. 9.17. CAR Genetic Variants (SNPs) and their Functional Consequences. 9.18. CAR Summary. 9.19. References. Chapter 10. Beyond PXR and CAR, Regulation of Xenobiotic Metabolism by Other Nuclear Receptors (Martin Wagner, Gernot Zollner, and Michael Trauner). 10.1. Introduction. 10.2. Farnesoid X Receptor. 10.3. Hepatocyte Nuclear Factor 4. 10.4. Vitamin D receptor. 10.5. Glucocorticoid Receptor. 10.6. Peroxisome Proliferator Activated Receptors. 10.7. Aryl Hydrocarbon Receptor (AhR). 10.8. Conclusions. 10.9. References. Chapter 11. Emerging Role of Retinoid-Related Orphan Receptor (ROR) and Its Crosst alk With LXR(Liver X Receptor) in the Regulation Of Drug-Metabolizing Enzymes (Taira Wada and Wen Xie). 11.1. Introduction. 11.2. Orphan Nuclear Receptor RORalpha. 11.3. A Potential Role of RORs in Xeno- and Endobiotic Gene Regulation. 11.4. LXR and its Regulation of Drug Metabolizing Enzymes. 11.5. A Functional Cross-Talk Between RORa and LXR in the Regulation of Xeno- and Endobiotic Genes. 11.6. Closing Remarks. Index.

Cannabidiol (CBD), a non-psychoactive phytocannabinoid of cannabis, is therapeutically used as an analgesic, anti-convulsant, anti-inflammatory, and anti-psychotic drug. There is a growing concern about the adverse side effects posed by CBD usage. Pregnane X receptor (PXR) is a nuclear receptor activated by a variety of dietary steroids, pharmaceutical agents, and environmental chemicals. In addition to the role in xenobiotic metabolism, the atherogenic and dyslipidemic effects of PXR have been revealed in animal models. CBD has a low affinity for cannabinoid receptors, thus it is important to elucidate the molecular mechanisms by which CBD activates cellular signaling and to assess the possible adverse impacts of CBD on pro-atherosclerotic events in cardiovascular system, such as dyslipidemia. Our study aims to explore the cellular and molecular mechanisms by which exposure to CBD activates human PXR and increases the risk of dyslipidemia. Both human hepatic and intestinal cells were used to test if CBD was a PXR agonist via cell-based transfection assay. The key residues within PXR's ligand-binding pocket that CBD interacted with were investigated using computational docking study together with site-directed mutagenesis assay. The C57BL/6 wildtype mice were orally fed CBD in the presence of PXR antagonist resveratrol (RES) to determine how CBD exposure could change the plasma lipid profiles in a PXR-dependent manner. Human intestinal cells were treated with CBD and/or RES to estimate the functions of CBD in cholesterol uptake. CBD was a selective agonist of PXR with higher activities on human PXR than rodents PXRs and promoted the dissociation of human PXR from nuclear co-repressors. The key amino acid residues Met246, Ser247, Phe251, Phe288, Trp299, and Tyr306 within PXR's ligand binding pocket were identified to be necessary for the agonistic effects of CBD. Exposure to CBD increased the circulating total cholesterol levels in mice which was partially caused by the induced expression levels of the key intestinal PXR-regulated lipogenic genes. Mechanistically, CBD induced the gene expression of key intestinal cholesterol transporters, which led to the increased cholesterol uptake by intestinal cells. CBD was identified as a selective PXR agonist. Exposure to CBD activated PXR signaling and increased the atherogenic cholesterol levels in plasma, which partially resulted from the ascended cholesterol uptake by intestinal cells. Our study provides potential evidence for the future risk assessment of CBD on cardiovascular disease, such as dyslipidemia.

The Pregnane X receptor (PXR) is a member of the nuclear receptor family, which is highly expressed in liver as well as in intestine and regulates the transcription of genes involved in the metabolism, transport and elimination of xenobiotics. Recently, the role of PXR and xenobiotic metabolism in regulating inflammation has become evident. Here we demonstrate that in addition to its role in xenosensing and drug metabolism, PXR signaling is also essential for mediating innate antimicrobial immune responses. Mice lacking PXR were highly susceptible to the intracellular bacteria Listeria Monocytogenes (LM). Bone marrow derived macrophages (BMDMs) from PXR-/- mice were proficient in internalizing bacteria, but incapable of clearing LM. Surprisingly, the over activation of Toll-like receptor 4 (TLR4) signaling in the absence of PXR was the singular determinant of susceptibility in PXR-/- mice since mice that were deficient in both PXR and TLR4 were efficient in clearing LM. Furthermore, administration of TLR4 specific inhibitors rescued the ability of PXR-/- mice and BMDMs to clear bacteria. Our results demonstrate an unexpected role of PXR in controlling innate immunity by negatively regulating TLR4 gene expression. In addition, our study has uncovered a remarkable impact of TLR4 signaling in driving the quality of antimicrobial immune response to gram-positive bacteria.

Interactions of pharmaceuticals and other xenobiotics on hepatic pregnane X receptor and cytochrome P450 3A signaling pathway in rainbow trout ( Oncorhynchus mykiss)

Xenobiotic receptors are traditionally defined as xenobiotic chemical-sensing receptors, the activation of which transcriptionally regulates the expression of enzymes and transporters involved in the metabolism and disposition of xenobiotics. Emerging evidence suggests that "xenobiotic receptors" also have diverse endobiotic functions, including their effects on lipid metabolism and energy metabolism. Dyslipidemia is a major risk factor forcardiovascular disease, diabetes, obesity, metabolic syndrome, stroke, nonalcoholic fatty liver disease (NAFLD), and nonalcoholic steatohepatitis (NASH). Understanding the molecular mechanism by which transcriptional factors, including the xenobiotic receptors, regulate lipid homeostasis will help to develop preventive and therapeutic approaches. This review describes recent advances in our understanding the atypical roles of three xenobiotic receptors: aryl hydrocarbon receptor (AhR), pregnane X receptor (PXR), and constitutive androstane receptor (CAR), in metabolic disorders, with a particular focus on their effects on lipid and glucose metabolism. Collectively, the literatures suggest the potential values of AhR, PXR and CAR as therapeutic targets for the treatment of NAFLD, NASH, obesity and diabetes, and cardiovascular diseases.

Targeting xenobiotic receptors PXR and CAR for metabolic diseases