Thiazolidinediones (TZDs) are potent insulin sensitizers that act through the nuclear receptor peroxisome proliferator-activated receptor-γ (PPARγ) and are highly effective oral medications for type 2 diabetes. However, their unique benefits are shadowed by the risk for fluid retention, weight gain, bone loss and congestive heart failure. This raises the question as to whether it is possible to build a safer generation of PPARγ-specific drugs that evoke fewer side effects while preserving insulin-sensitizing potential. Recent studies that have supported the continuing physiologic and therapeutic relevance of the PPARγ pathway also provide opportunities to develop newer classes of molecules that reduce or eliminate adverse effects. This review highlights key advances in understanding PPARγ signaling in energy homeostasis and metabolic disease and also provides new explanations for adverse events linked to TZD-based therapy.

The circadian clock acts at the genomic level to coordinate internal behavioral and physiologic rhythms via the CLOCK-BMAL transcriptional heterodimer. Although the nuclear receptors REV-ERBα and β have been proposed to form an accessory feedback loop that contributes to clock function1,2, their precise roles and importance remain unresolved. To establish their regulatory potential we generated comparative cistromes of both REV-ERB isoforms, which revealed shared recognition at over 50% of their total sites and extensive overlap with the master circadian regulator BMAL1. While Rev-erbα has been shown to directly regulate Bmal1 expression1,2, the cistromic analysis reveals a direct connection between Bmal1 and Rev-erbα and β regulatory circuits than previously suspected. Genes within the intersection of the BMAL1, REV-ERBα and REV-ERBβ cistromes are highly enriched for both clock and metabolic functions. As predicted by the cistromic analysis, dual depletion of Rev-erbα/β function by creating double-knockout mice (DKOs) profoundly disrupted circadian expression of core circadian clock and lipid homeostatic gene networks. As a result, DKOs show strikingly altered circadian wheel-running behavior and deregulated lipid metabolism. These data now ally Rev-erbα/β with Per, Cry and other components of the principal feedback loop that drives circadian expression and suggest a more integral mechanism for the coordination of circadian rhythm and metabolism.

Summary The poor clinical outcome in pancreatic ductal adenocarcinoma (PDA) is attributed to intrinsic chemoresistance and a growth-permissive tumor microenvironment. Conversion of quiescent to activated pancreatic stellate cells (PSCs) drives the severe stromal reaction that characterizes PDA. Here we reveal that the vitamin D receptor (VDR) is expressed in stroma from human pancreatic tumors and that treatment with the VDR ligand calcipotriol markedly reduced markers of inflammation and fibrosis in pancreatitis and human tumor stroma. We show that VDR acts as a master transcriptional regulator of PSCs to reprise the quiescent state resulting in induced stromal remodeling, increased intratumoral gemcitabine, reduced tumor volume and a 57% increase in survival compared to chemotherapy alone. This work describes a molecular strategy through which transcriptional reprogramming of tumor stroma enables chemotherapeutic response and suggests Vitamin D priming as an adjunct in PDA therapy.

Nonalcoholic steatohepatitis (NASH) is often linked with disorders that are clearly associated with insulin resistance (IR): obesity, type 2 diabetes mellitus, and hypertriglyceridemia. We tested the hypotheses that (1) IR is an essential requirement for the development of NASH and (2) a high association between IR and liver disease is relatively specific for NASH. We measured body mass index (BMI), waist/hip ratio, and fasting serum lipid, insulin, C-peptide, and glucose levels in 66 patients with NASH (21 with advanced fibrosis and 45 with mild fibrosis). IR was determined by the homeostasis model assessment (HOMA). We also determined the strength of the association of NASH with insulin resistance syndrome (IRS) as defined by World Health Organization criteria. To assess whether the finding of IR was relatively specific to NASH rather than simply to obesity or liver disease, we compared the results of a subset of 36 patients with less-severe NASH with 36 age-and sex-matched patients with chronic hepatitis C virus (HCV) of comparable fibrotic severity. IR was confirmed in 65 patients (98%) with NASH, and 55 (87%) fulfilled minimum criteria for IRS. IR was found in lean as well as in overweight and obese patients. The IR values and the prevalence of IRS (75% vs. 8.3%) were significantly higher in those with NASH than in comparable cases of HCV. Hyperinsulinemia was attributable to increased insulin secretion rather than decreased hepatic extraction. N onalcoholic steatohepatitis (NASH) is characterized by morphological features indistinguishable from alcoholic liver disease in individuals who do not consume excess alcohol. 1 NASH can progress to cirrhosis, and death from liver failure is now the second-leading cause of death in these patients. 2 Although the prevalence of NASH appears to be increasing, the etiopathogenesis remains poorly understood.Associations with drug toxicity, weight-reducing operations, lipodystrophy, and other uncommon inherited syndromes are well documented but are rarely present in most patients with NASH. [1][2][3][4][5][6][7][8] Rather, attention has been drawn to the increased prevalence of common metabolic disorders in the "typical" patient with NASH. [1][2][3][4][5][6][7] Autopsy data indicate that NASH is at least 6 times more prevalent in obese individuals compared with lean subjects. 7 Type 2 diabetes mellitus or abnormalities of glucose tolerance are present in up to one third of patients with NASH, 8 often with hypertriglyceridemia and/or hypercholesterolemia. 9,10 The above metabolic disorders are also cardiovascular risk factors and often cluster together as syndrome X, which includes impaired glucose tolerance, dyslipidemia, and hypertension. 11 This disease cluster is also referred to as the metabolic or insulin resistance syndrome (IRS); the latter highlights a central role for insulin resistance (IR) in this disorder. 12,13 The expanded formulation of IRS includes central (visceral or truncal) adiposity, lipid abnormalities, hyperuricemia, polycystic ovarian syndrome, and...

Xenobiotics induce the transcription of cytochromes P450 (CYPs) 2B and 3A through the constitutive androstane receptor (CAR; NR1I3) and pregnane X receptor (PXR; NR1I2), respectively. In this report, we have systematically compared a series of xenobiotics and natural steroids for their effects on mouse and human CAR and PXR. Our results demonstrate dual regulation of PXR and CAR by a subset of compounds that affect CYP expression. Moreover, there are marked pharmacological differences between the mouse (m) and human (h) orthologs of both CAR and PXR. For example, the planar hydrocarbon 1,4-bis[2-(3,5-dichloropyridyl-oxy-)]benzene activates mCAR and hPXR but has little or no activity on hCAR and mPXR. In contrast, the CAR deactivator androstanol activates both mouse and human PXR. Similarly, the PXR activator clotrimazole is a potent deactivator of hCAR. Using radioligand binding and fluorescence resonance energy transfer assays, we demonstrate that several of the compounds that regulate mouse and human CAR, including natural steroids, bind directly to the receptors. Our results suggest that CAR, like PXR, is a steroid receptor that is capable of recognizing structurally diverse compounds. Moreover, our findings underscore the complexity in the physiologic response to xenobiotics.

Cytochrome P-450 3A4 (CYP3A4), the predominant cytochrome P-450 expressed in adult human liver, is subject to transcriptional induction by a variety of structurally unrelated xenobiotics, including the antibiotic rifampicin. The molecular mechanisms underlying this phenomenon are poorly understood. We transfected a human liver-derived cell line (HepG2) with various CYP3A4-luciferase reporter gene constructs containing a nested set of 5'-deletions of the CYP3A4 5'-flanking region. Rifampicin-inducible transcription of the reporter gene was observed only with the longest construct, which encompassed bases -13000 to +53 of CYP3A4 (3-fold induction). The responsive region was functional regardless of its position or orientation relative to the proximal promoter of CYP3A4 and was capable of conferring rifampicin-inducible expression on a heterologous promoter. Further deletion mutants localized the induction to bases -7836 to -7607. In vitro DNase I footprint analysis of this region revealed four protected sites (FP1, FP2, FP3, and FP4). Two of these sites, FP3 (bases -7738 to -7715) and FP4 (bases -7698 to -7682), overlapped binding motifs for the orphan human pregnane X receptor (hPXR). Cotransfection of responsive constructs with a hPXR expression vector substantially increased the rifampicin-inducibility to approximately 50-fold. In addition, the rifampicin-responsive constructs were strongly activated by a range of CYP3A inducers. Finally, we demonstrate cooperativity between elements within the distal enhancer region and cis-acting elements in the proximal promoter of CYP3A4. Our results provide evidence for the existence of a potent enhancer module, 8 kb distal to the transcription start point, which mediates the transcriptional induction of CYP3A4 by activators of hPXR.

The systemic expression of the bile acid (BA) sensor farnesoid X receptor (FXR) has led to promising new therapies targeting cholesterol metabolism, triglyceride production, hepatic steatosis and biliary cholestasis. In contrast to systemic therapy, bile acid release during a meal selectively activates intestinal FXR. By mimicking this tissue-selective effect, the gut-restricted FXR agonist fexaramine (Fex) robustly induces enteric fibroblast growth factor 15 (FGF15), leading to alterations in BA composition, but does so without activating FXR target genes in the liver. However, unlike systemic agonism, we find that Fex reduces diet-induced weight gain, body-wide inflammation and hepatic glucose production, while enhancing thermogenesis and browning of white adipose tissue (WAT). These pronounced metabolic improvements suggest tissue-restricted FXR activation as a new approach in the treatment of obesity and metabolic syndrome.

SUMMARY Liver fibrosis is a reversible wound-healing response involving TGFβ1 activation of hepatic stellate cells (HSCs). Here we show that vitamin D receptor (VDR) ligands inhibit HSC activation and abrogate liver fibrosis, while Vdr knockout mice spontaneously developed hepatic fibrosis. Mechanistically, we describe a pronounced redistribution of genome wide VDR binding sites (VDR cistrome) in HSCs elicited by a TGFβ1 pro-fibrotic insult. This TGFβ1-induced VDR cistrome overlaps extensively with SMAD3 binding sites, with co-occupancy at numerous cis-regulatory elements identified on a large set of pro-fibrotic genes. Addition of VDR ligand reduces SMAD3 occupancy at co-regulated genes, revealing an intersecting VDR/SMAD genomic circuit that regulates hepatic fibrogenesis. These results define a role for VDR as a endocrine checkpoint to modulate the wound healing response in liver, and suggest VDR ligands as a potential therapy for liver fibrosis.