Xenobiotic receptors

Division Of Basic Sciences - Nci

Investigators

Linked publications, trials & patents

Abstract

Project 1, PPARalpha and CYP2E1: : Introduction Obesity and the associated metabolic disorders are increasing at an alarming rate globally. An imbalance between energy intake and expenditure results in obesity, and adipose browning induction is one attractive strategy in rodent models for enhancing non-shivering thermogenesis and thus countering the excess energy intake. Nuclear receptors have become drug targets for the treatment of metabolic diseases, although less is known about their roles in the modulation of adipose browning. Cytochrome P450 (CYP) 2E1 expression was suggested to be closely related to the pathological process of metabolic diseases. CYP2E1 activity is significantly increased in both humans and experimental rodent models under conditions of diabetes, fasting, obesity, and high-fat diet (HFD) treatment. Cyp2e1-null mice are protected from HFD-induced obesity and nonalcoholic steatohepatitis. Peroxisome proliferator-activated receptor alpha (PPARalpha) plays an essential role in lipid homeostasis and energy regulation, and the expression and excretion of hepatic fibroblast growth factor (FGF)21, a major PPARalpha target gene in liver, could act as an endocrinal beige stimulator to alleviate the obesity. However, the mechanism by which CYP2E1 affects metabolic diseases has not been explored. CYP2E1, a member of the CYP superfamily, was initially identified as an ethanol-inducible enzyme involved in the metabolism of various low-molecular weight xenobiotics including ethanol, benzene, carbon tetrachloride, and acetaminophen. Notably beyond these xenobiotics, CYP2E1 also metabolizes endogenous substrates including fatty acids, while various endogenous ligands also including fatty acids were reported to activate PPARalpha. Thus, it is possible that some of the endogenous substrates of CYP2E1 also serve as PPARalpha agonists. However, how the shared substrates and ligands of CYP2E1 and PPARalpha could act as signaling-transducing molecules in modulating the metabolic diseases are largely unknown. To explore the potential crosstalk between CYP2E1 and PPARalpha, global genomics, metabolomics in combination with Cyp2e1-null mice and liver-specific Ppara-null mice as well as the CYP2E1 inhibitor diethyldithiocarbamate were employed to uncover whether and how CYP2E1 deficiency decreased obesity by modulating white adipose browning through the CYP2E-PPARalpha crosstalk with shared substrates as signaling-transducing molecules. Results. Although the functions of metabolic enzymes and nuclear receptors in controlling physiological homeostasis have been established, their crosstalk in modulating metabolic disease has not been explored. Genetic ablation of the xenobiotic-metabolizing cytochrome P450 enzyme CYP2E1 in mice markedly induced adipose browning and increased energy expenditure to improve obesity. CYP2E1 deficiency activated the expression of hepatic peroxisome proliferator-activated receptor alpha (PPARalpha) target genes, including fibroblast growth factor (FGF)21, that upon release from the liver, enhanced adipose browning and energy expenditure to decrease obesity. Nineteen metabolites were increased in Cyp2e1-null mice as revealed by global untargeted metabolomics, among which four compounds, lysophosphatidylcholine and three polyunsaturated fatty acids were found to be directly metabolized by CYP2E1 and to serve as PPARalpha agonists, thus explaining how CYP2E1 deficiency causes hepatic PPARalpha activation through increasing cellular levels of endogenous PPARalpha agonists. Translationally, a CYP2E1 inhibitor was found to activate the PPARalpha-FGF21-beige adipose axis and decrease obesity in wild-type mice, but not in liver-specific Ppara-null mice. The present results establish a metabolic crosstalk between PPARalpha and CYP2E1 that supports the potential for a novel anti-obesity strategy of activating adipose tissue browning by targeting the CYP2E1 to modulate endogenous metabolites beyond its canonical role in xenobiotic-metabolism. Project 2, PPARalpha and FABP1: Introduction. Nonalcoholic fatty liver disease (NAFLD) is a common chronic liver diseases. Persistent NAFLD could progress to nonalcoholic steatohepatitis (NASH) and increase the risk of the end-stage liver diseases such as cirrhosis and hepatocellular carcinoma. To date, no drug has been approved for the treatment of NASH, and thus, pharmacological therapies for NASH treatment are warranted. PPARalpha agonists such as fibrates are widely prescribed for the treatment of dyslipidemias as lipid-lowering drugs in clinic, however, their use in human NASH treatment has not been approved. Global PPARalpha knockout in mice markedly enhances NASH but protects against insulin resistance. suggesting the pleiotropic roles of PPARalpha. Hepatocyte-specific PPARalpha knockout was found to only partially phenocopy the phenotype of global PPARalpha knockout in NAFLD and fasting-induced hepatic steatosis. Understanding the tissue-specific role of extrahepatic PPARalpha may guide drug discovery from PPARalpha modulators. Dietary fat is absorbed by the enterocytes in the form of free fatty acids and 2-monoacylglycerols that are produced from dietary triglycerides (TG), while the absorbed fatty acids and monoacylglycerols are re-esterified into TG and exported to the blood. Fatty acid-binding protein 1 (FABP1) is known to facilitate transport of fatty acids and other hydrophobic molecules in the liver, while the role of intestinal FABP1 in modulating dietary fat absorption and NASH is still unknown. Results. The role of intestine PPARalpha-FABP1 signaling in modulating the NASH progression was studied using intestine-specific PPARalpha or FABP1 knockout mice, intestine-specific PPARalpha/FABP1 double knockout mice, PPARA-humanized mice, PPRE-Luc mice, primary intestinal organoids, and PPARalpha-specific antagonist GW6471 in combination with global transcriptome and molecular biological analyses. Correlative studies on PPARalpha/FABP1 signaling with obesity were carried out on human intestine samples. Peroxisome proliferator-activated receptor alpha (PPARalpha) regulates fatty acid transport and catabolism in liver. However, the role of intestinal PPARalpha in lipid homeostasis is largely unknown. Here, intestinal PPARalpha was examined for its modulation of obesity and nonalcoholic steatohepatitis (NASH). Intestinal PPARalpha was activated and FABP1 upregulated in obese humans and high-fat diet-fed mice by using human intestine specimens or high-fat diet (HFD) or high-fat, high-cholesterol, high-fructose diet (HFCFD)-fed C57BL/6N mice or PPARA-humanized PPRE-Luciferase mice. Intestine-specific Ppara or Fabp1 disruption in mice fed a HFD or HFCFD decreased obesity-associated metabolic disorders and NASH. Molecular analyses by luciferase reporter assays and chromatin-immunoprecipitation assays in combination with fatty acid uptake assay in primary intestinal organoids revealed that intestinal PPARalpha targeted FABP1 that mediated the effects of intestinal PPARalpha in modulating fatty acid uptake. The PPARalpha antagonist GW6471 improved obesity and NASH, dependent on intestinal PPARalpha or FABP1. PPARalpha and FABP1 double-knockout mice revealed that intestinal Ppara disruption failed to further decrease obesity and NASH in the absence of intestinal FABP1. Translationally, GW6471 reduced human PPARA-driven intestinal fatty acid uptake and improved obesity-related metabolic dysfunctions in PPARA-humanized, but not Ppara-null, mice. This study revealed t *TRUNCATED*