Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that are involved in regulating glucose and lipid homeostasis, inflammation, proliferation and differentiation. Although all of these functions might contribute to the influence of PPARs in carcinogenesis, there is a distinct need for a balanced review of the literature and additional experimentation to determine the potential for targeting PPARs for cancer therapy and cancer chemoprevention. As PPAR agonists include drugs used for the treatment of metabolic diseases, a more complete understanding of the roles of PPARs in cancer will aid in determining any increased cancer risk for patients undergoing therapy with PPAR agonists.

Possible prevention and therapeutic intervention strategies to counteract acetaminophen (APAP) hepatotoxicity would be of great value. Wuzhi tablet (WZ, extract of Schisandrae sphenanthera) possesses hepatoprotective effects against hepatitis and the hepatic dysfunction induced by various chemical hepatotoxins. In this study, the protective effect of WZ on APAP-induced hepatic injury was evaluated and targeted metabolomics by LC-MS-based metabolomics was used to examine whether WZ influences hepatic metabolism. The results demonstrated significant hepatoprotection of WZ against APAP-induced liver injury; pretreatment with WZ prior to APAP administration blocks the increase in serum palmitoylcarnitine and oleoylcarnitine and thus restores the APAP-impaired fatty acid β-oxidation to normal levels. These studies further revealed a significant and prolonged upregulation of the PPARα target genes Cpt1 and Acot1 by WZ mainly contributing to the maintenance of normal fatty acid metabolism and thus potentially contributing to the hepatic protection of WZ against APAP-induced hepatic toxicity. Taken together, the current study provides new insights into understanding the hepatoprotective effect of WZ against APAP-induced liver toxicity.

Cytochrome P450 1B1 contributes to the development of angiotensin II-induced hypertension and associated cardiovascular pathophysiology. In view of the critical role of angiotensin II in the kidney, as well as in salt and water homeostasis, and blood pressure regulation, we determined the contribution of cytochrome P450 1B1 to renal dysfunction and injury associated with angiotensin II-induced hypertension in male Cyp1b1+/+ and Cyp1b1−/− mice. Angiotensin II infusion (700 ng/kg/min) given by miniosmotic pumps for 13 and 28 days increased systolic blood pressure in Cyp1b1+/+ mice; this increase was significantly reduced in Cyp1b1−/− mice. Angiotensin II increased renal Cyp1b1 activity, vascular resistance and reactivity to vasoconstrictor agents, and caused endothelial dysfunction in Cyp1b1+/+ but not Cyp1b1−/− mice. Angiotensin II increased water consumption and urine output, decreased urine osmolality, increased urinary Na+ and K+ excretion, and caused proteinuria and albuminuria in Cyp1b1+/+ mice that was diminished in Cyp1b1−/− mice. Infusion of angiotensin II for 28, but not 13 days, caused renal fibrosis, tubular damage and inflammation in Cyp1b1+/+ mice, which was minimized in Cyp1b1−/− mice. Angiotensin II increased levels of 12- and 20-hydroxyeicosatetraenoic acids; reactive oxygen species; and activity of NADPH oxidase, ERK1/2, p38 MAPK, and c-Src in the kidneys of Cyp1b1+/+ but not Cyp1b1−/− mice. These data suggest that increased thirst, renal dysfunction, and injury and inflammation associated with angiotensin II-induced hypertension in mice depend on cytochrome P450 1B1 activity thus indicating that cytochrome P450 1B1 could serve as a novel target for treating renal disease and hypertension.

Aims

Hypoxia-inducible factor 1 (HIF-1) is a heterodimer composed of HIF-1α and HIF-1β subunits. HIF-1 is known to promote tissue vascularization by activating the transcription of genes encoding angiogenic factors, which bind to receptors on endothelial cells (ECs) and bone marrow-derived angiogenic cells (BMDACs). In this study, we analysed whether HIF-1 activity in the responding ECs and BMDACs is also required for cutaneous vascularization during burn wound healing.

Methods and results

We generated mice with floxed alleles at the Hif1a or Arnt locus encoding HIF-1α and HIF-1β, respectively. Expression of Cre recombinase was driven by the Tie2 gene promoter, which is expressed in ECs and bone marrow cells. Tie2Cre+ and Tie2Cre− mice were subjected to burn wounds of reproducible diameter and depth. Deficiency of HIF-1α or HIF-1β in Tie2-lineage cells resulted in delayed wound closure, reduced vascularization, decreased cutaneous blood flow, impaired BMDAC mobilization, and decreased BMDAC homing to burn wounds.

Conclusion

HIF-1 activity in Tie2-lineage cells is required for the mobilization and homing of BMDACs to cutaneous burn wounds and for the vascularization of burn wound tissue.

Previously, we showed that the cytochrome P450 1B1 inhibitor, 2,3´,4,5´-tetramethoxystilbene, reversed DOCA-salt induced hypertension and minimized endothelial and renal dysfunction in the rat. This study was conducted to test the hypothesis that cytochrome P450 1B1 contributes to cardiac dysfunction, and renal damage and inflammation associated with DOCA-salt-induced hypertension, via increased production of reactive oxygen species, and modulation of neurohumoral factors and signaling molecules. DOCA-salt increased systolic blood pressure, cardiac and renal cytochrome P450 1B1 activity, and plasma levels of catecholamines, vasopressin, and endothelin-1 in wild type (Cyp1b1+/+) mice that were minimized in Cyp1b1−/− mice. Cardiac function, assessed by echocardiography, showed that DOCA-salt increased the thickness of the left ventricular posterior and anterior walls during diastole, the left ventricular internal diameter, and end-diastolic and end-systolic volume in Cyp1b1+/+ but not Cyp1b1−/− mice; stroke volume was not altered in either genotype. DOCA-salt increased renal vascular resistance and caused vascular hypertrophy, renal fibrosis, increased renal infiltration of macrophages and T-lymphocytes, caused proteinuria, increased cardiac and renal NADPH oxidase activity, production of reactive oxygen species, and activities of ERK1/2, p38 MAPK and c-Src; these were all reduced in DOCA-salt-treated Cyp1b1−/− mice. Renal and cardiac levels of eicosanoids were not altered in either genotype of mice. These data suggest that in DOCA-salt hypertension in mice, cytochrome P450 1B1 plays a pivotal role in cardiovascular dysfunction, renal damage and inflammation, and increased levels of catecholamines, vasopressin, and endothelin-1, consequent to generation of reactive oxygen species and activation of ERK1/2, p38 MAPK, and c-Src independent of eicosanoids.

Peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) function and receptor cross-talk with other nuclear receptors, including PPARγ and retinoic acid receptors (RARs), was examined using stable human HaCaT keratinocyte cell lines over-expressing PPARβ/δ or PPARγ. Enhanced ligand-induced expression of two known PPAR target genes, adipocyte differentiation-related protein (ADRP) and angiopoietin-like protein 4 (ANGPTL4), was found in HaCaT keratinocytes over-expressing PPARβ/δ or PPARγ. Over-expression of PPARβ/δ did not modulate the effect of a PPARγ agonist on up-regulation of ADRP or ANGPTL4 mRNA in HaCaT keratinocytes. All-trans retinoic acid (atRA) increased expression of a known RAR target gene, yet despite a high ratio of fatty acid binding protein 5 (FABP5) to cellular retinoic acid binding protein II, did not increase expression of ANGPTL4 or 3-phosphoinositide-dependent-protein kinase 1 (PDPK1), even in HaCaT keratinocytes expressing markedly higher levels of PPARβ/δ. While PPARβ/δ-dependent attenuation of staurosporine- or UVB-induced poly (ADP-ribose) polymerase (PARP) cleavage was not observed, PPARβ/δ- and PPARγ-dependent repression of UVB-induced expression and secretion of inflammatory cytokines was found in HaCaT keratinocytes over-expressing PPARβ/δ or PPARγ. These studies suggest that FABP5 does not transport atRA or GW0742 to PPARβ/δ and promote anti-apoptotic activity by increasing expression of PDPK1, or that PPARβ/δ interferes with PPARγ transcriptional activity. However, these studies demonstrate that stable over-expression of PPARβ/δ or PPARγ significantly increases the efficacy of ligand activation and represses UVB-induced expression of tumor necrosis factor α (TNFα), interleukin 6 (IL6), or IL8 in HaCaT keratinocytes, thereby establishing an excellent model to study the functional role of these receptors in human keratinocytes.

Peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) is a promising drug target since its agonists increase serum high-density lipoprotein; decrease low-density lipoprotein, triglycerides, and insulin associated with metabolic syndrome; improve insulin sensitivity; and decrease high fat diet-induced obesity. PPARβ/δ agonists also promote terminal differentiation and elicit anti-inflammatory activities in many cell types. However, it remains to be determined whether PPARβ/δ agonists can be developed as therapeutics because there are reports showing either pro- or anti-carcinogenic effects of PPARβ/δ in cancer models. This review examines studies reporting the role of PPARβ/δ in colon, breast, and lung cancers. The prevailing evidence would suggest that targeting PPARβ/δ is not only safe but could have anti-carcinogenic protective effects.

The role of peroxisome proliferator-activated receptor β/δ (PPARβ/δ) in Harvey sarcoma ras (Hras)-expressing cells was examined. Ligand activation of PPARβ/δ caused a negative selection with respect to cells expressing higher levels of the Hras oncogene by inducing a mitotic block. Mitosis-related genes that are predominantly regulated by E2F were induced to a higher level in HRAS-expressing Pparβ/δ-null keratinocytes compared to HRAS-expressing wild-type keratinocytes. Ligand-activated PPARβ/δ repressed expression of these genes by direct binding with p130/p107, facilitating nuclear translocation and increasing promoter recruitment of p130/p107. These results demonstrate a novel mechanism of PPARβ/δ cross talk with E2F signaling. Since cotreatment with a PPARβ/δ ligand and various mitosis inhibitors increases the efficacy of increasing G2/M arrest, targeting PPARβ/δ in conjunction with mitosis inhibitors could become a suitable option for development of new multitarget strategies for inhibiting RAS-dependent tumorigenesis.

Critical physiological roles of peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) include the regulation glucose and lipid homeostasis, cellular differentiation, and modulation of inflammation. The potential for targeting PPARβ/δ for the prevention and treatment of metabolic diseases or cancer, is compromised because of major inconsistencies in the literature. This is due primarily to uncertainty regarding the effect of PPARβ/δ and its activation on cell proliferation, apoptosis and cell survival. This review summarizes both the confirmed and conflicting mechanisms that have been described for PPARβ/δ and the potential for targeting this nuclear receptor for the prevention and treatment of colon cancer.

Autosomal Dominant Polycystic Kidney Disease (ADPKD; MIM ID's 173900, 601313, 613095) leads to end-stage kidney disease, caused by mutations in PKD1 or PKD2. Inactivation of Pkd1 before or after P13 in mice results in distinct early- or late-onset disease. Using a mouse model of ADPKD carrying floxed Pkd1 alleles and an inducible Cre recombinase, we intensively analyzed the relationship between renal maturation and cyst formation by applying transcriptomics and metabolomics to follow disease progression in a large number of animals induced before P10. Weighted gene co-expression network analysis suggests that Pkd1-cystogenesis does not cause developmental arrest and occurs in the context of gene networks similar to those that regulate/maintain normal kidney morphology/function. Knowledge-based Ingenuity Pathway Analysis (IPA) software identifies HNF4α as a likely network node. These results are further supported by a meta-analysis of 1,114 published gene expression arrays in Pkd1 wild-type tissues. These analyses also predict that metabolic pathways are key elements in postnatal kidney maturation and early steps of cyst formation. Consistent with these findings, urinary metabolomic studies show that Pkd1 cystic mutants have a distinct profile of excreted metabolites, with pathway analysis suggesting altered activity in several metabolic pathways. To evaluate their role in disease, metabolic networks were perturbed by inactivating Hnf4α and Pkd1. The Pkd1/Hnf4α double mutants have significantly more cystic kidneys, thus indicating that metabolic pathways could play a role in Pkd1-cystogenesis.

Author Summary

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is the most common genetic cause of polycystic kidney disease and is responsible for 4.6% of the end-stage renal disease (ESRD) cases in the United States. It is most often caused by mutation in the PKD1 gene. To understand this disease, we made a mouse model in which we could delete the Pkd1 gene and study the animal as its kidney becomes cystic. Using this model, we had previously found that the maturation status of the animal determines whether cysts form within days or within months, and we had narrowed down this switch to a two-day interval. In the current study, we used the rapid cyst-forming model to analyze the expression pattern of thousands of genes in mutant and control kidneys, and metabolites excreted in the urine. Our results identify a number of genes that may be involved in cyst formation and suggest that metabolic changes may play a role in ADPKD and could alter disease progression. These analyses also predict that metabolic pathways are key elements in normal postnatal kidney maturation.

Background

The present study coupled expression profiling with chromatin immunoprecipitation sequencing (ChIP-seq) to examine peroxisome proliferator-activated receptor-β/δ (PPARβ/δ)-dependent regulation of gene expression in mouse keratinocytes, a cell type that expresses PPARβ/δ in high concentration.

Results

Microarray analysis elucidated eight different types of regulation that modulated PPARβ/δ-dependent gene expression of 612 genes ranging from repression or activation without an exogenous ligand, repression or activation with an exogenous ligand, or a combination of these effects. Bioinformatic analysis of ChIP-seq data demonstrated promoter occupancy of PPARβ/δ for some of these genes, and also identified the presence of other transcription factor binding sites in close proximity to PPARβ/δ bound to chromatin. For some types of regulation, ATF4 is required for ligand-dependent induction of PPARβ/δ target genes.

Conclusions

PPARβ/δ regulates constitutive expression of genes in keratinocytes, thus suggesting the presence of one or more endogenous ligands. The diversity in the types of gene regulation carried out by PPARβ/δ is consistent with dynamic binding and interactions with chromatin and indicates the presence of complex regulatory networks in cells expressing high levels of this nuclear receptor such as keratinocytes. Results from these studies are the first to demonstrate that differences in DNA binding of other transcription factors can directly influence the transcriptional activity of PPARβ/δ.

There has been limited analysis of the effects of hepatocellular carcinoma (HCC) on liver metabolism and circulating endogenous metabolites. Here we report the findings of a plasma metabolomic investigation of HCC patients using ultraperformance liquid chromatography-electrospray ionization-quadrupole mass spectrometry (UPLC-ESI-QTOFMS), random forests machine learning algorithm and multivariate data analysis. Control subjects included healthy individuals as well as patients with liver cirrhosis or acute myeloid leukemia. We found that HCC was associated with increased plasma levels of glycodeoxycholate, deoxycholate 3-sulfate and bilirubin. Accurate mass measurement also indicated upregulation of biliverdin and the fetal bile acids 7α-hydroxy-3-oxochol-4-en-24-oic acid and 3-oxochol-4,6-dien-24-oic acid in HCC patients. A quantitative lipid profiling of patient plasma was also performed using ultra-performance liquid chromatography-electrospray ionization-triple quadrupole mass spectrometry (UPLC-ESI-TQMS). Using this method we found that that HCC was associated also with reduced levels of lysophosphocholines (LPC) and in 4/20 patients with increased levels of lysophosphatidic acid (LPA(16:0)), where it correlated with plasma α-fetoprotein levels. Interestingly, when fatty acids were quantitatively profiled by gas chromatography-mass spectrometry (GCMS), we found that lignoceric acid (24:0) and nervonic acid (24:1) were virtually absent from HCC plasma. Overall, this investigation illustrates the power of the new discovery technologies represented in the UPLC-ESI-QTOFMS platform combined with the targeted, quantitative platforms of UPLC-ESI-TQMS and GCMS for conducting metabolomic investigations that can engender new insights into cancer pathobiology.

This study critically examined the role of PPARβ/δ in colon cancer models. Expression of PPARβ/δ mRNA and protein was lower and expression of CYCLIN D1 protein higher in human colon adenocarcinomas compared to matched non-transformed tissue. Similar results were observed in colon tumors from Apc+/Min-FCCC mice compared to control tissue. Dietary administration of sulindac to Apc+/Min-FCCC mice had no influence on expression of PPARβ/δ in normal colon tissue or colon tumors. Cleaved poly (ADP-ribose) polymerase (PARP) was either increased or unchanged, while expression of 14-3-3ε was not influenced in human colon cancer cell lines cultured with the PPARβ/δ ligand GW0742 under conditions known to increase apoptosis. While DLD1 cells exhibited fewer early apoptotic cells after ligand activation of PPARβ/δ following treatment with hydrogen peroxide, this change was associated with an increase in late apoptotic/necrotic cells, but not an increase in viable cells. Stable over-expression of PPARβ/δ in human colon cancer cell lines enhanced ligand activation of PPARβ/δ and inhibition of clonogenicity in HT29 cells. These studies are the most quantitative to date to demonstrate that expression of PPARβ/δ is lower in human and Apc+/Min-FCCC mouse colon tumors than in corresponding normal tissue, consistent with the finding that increasing expression and activation of PPARβ/δ in human colon cancer cell lines inhibits clonogenicity. Because ligand-induced attenuation of early apoptosis can be associated with more late, apoptotic/necrotic cells, but not more viable cells, these studies illustrate why more comprehensive analysis of PPARβ/δ-dependent modulation of apoptosis is required in the future.

OBJECTIVE

Obesity, insulin resistance, and type 2 diabetes form a tightly correlated cluster of metabolic disorders in which adipose is one of the first affected tissues. The role of hypoxia and hypoxia-inducible factor 1 (HIF1) in the development of high-fat diet (HFD)–induced obesity and insulin resistance was investigated using animal models.

RESEARCH DESIGN AND METHODS

Mice with adipocyte-specific targeted disruption of the genes encoding the HIF1 obligatory subunits Hif1α or Arnt (Hif1β) were generated using an aP2-Cre transgene with the Cre/LoxP system. The mice were fed an HFD for 12 weeks and their metabolic phenotypes were determined. Gene expression patterns in adipose tissues were also determined by microarray and quantitative PCR.

RESULTS

On an HFD, adipocyte-specific ARNT knockout mice and adipocyte-specific HIF1α knockout mice exhibit similar metabolic phenotypes, including reduced fat formation, protection from HFD-induced obesity, and insulin resistance compared with similarly fed wild-type controls. The cumulative food intake remained similar; however, the metabolic efficiency was lower in adipocyte-specific HIF1α knockout mice. Moreover, indirect calorimetry revealed respiratory exchange ratios were reduced in adipocyte-specific HIF1α knockout mice. Hyperinsulinemic-euglycemic clamp studies demonstrated that targeted disruption of HIF1α in adipocytes enhanced whole-body insulin sensitivity. The improvement of insulin resistance is associated with decreased expression of Socs3 and induction of adiponectin.

CONCLUSIONS

Inhibition of HIF1 in adipose tissue ameliorates obesity and insulin resistance. This study reveals that HIF1 could provide a novel potential therapeutic target for obesity and type 2 diabetes.

Since the development and prognosis of alcohol-induced liver disease (ALD) vary significantly with genetic background, identification of a genetic background-independent noninvasive ALD biomarker would significantly improve screening and diagnosis. This study explored the effect of genetic background on the ALD-associated urinary metabolome using the Ppara-null mouse model on two different backgrounds, C57BL/6 (B6) and 129/SvJ (129S), along with their wild-type counterparts. Reversed-phase gradient UPLC-ESI-QTOF-MS analysis revealed that urinary excretion of a number of metabolites, such as, ethylsulfate, 4-hydroxyphenylacetic acid, 4-hydroxyphenylacetic acid sulfate, adipic acid, pimelic acid, xanthurenic acid, and taurine were background-dependent. Elevation of ethyl-β-D-glucuronide and N-acetylglycine was found to be common signature of the metabolomic response to alcohol exposure in wild-type as well as in Ppara-null mice of both strains. However, increased excretion of indole-3-lactic acid and phenyllactic acid was found to be a conserved feature exclusively associated with the alcohol-treated Ppara-null mouse on both backgrounds that develop liver pathologies similar to the early stages of human ALD. These markers reflected the biochemical events associated with early stages of ALD pathogenesis. The results suggest that indole-3-lactic acid and phenyllactic acid are potential candidates for conserved and pathology-specific high-throughput noninvasive biomarkers for early stages of ALD.

Oxygen dynamics in the liver is a central signaling mediator controlling hepatic homeostasis, and dysregulation of cellular oxygen is associated with liver injury. Moreover, the transcription factor relaying changes in cellular oxygen levels, hypoxia-inducible factor (HIF), is critical in liver metabolism and sustained increase in HIF signaling can lead to spontaneous steatosis, inflammation, and liver tumorigenesis. However, the direct responses and genetic networks regulated by HIFs in the liver are unclear. To help define the HIF signal transduction pathway, an animal model of HIF overexpression was generated and characterized. In this model, overexpression was achieved by Von Hippel-Lindau (Vhl) disruption in a liver-specific temporal fashion. Acute disruption of Vhl induced hepatic lipid accumulation in a HIF-2α-dependent manner. In addition, HIF-2α activation rapidly increased liver inflammation and fibrosis demonstrating that steatosis and inflammation are primary responses of the liver to hypoxia. To identify downstream effectors, a global microarray expression analysis was performed using livers lacking Vhl for 24-hours and 2-weeks, revealing a time-dependent effect of HIF on gene expression. Increase in genes involved in fatty acid synthesis were followed by an increase in fatty acid uptake-associated genes, and an inhibition of fatty acid β-oxidation. A rapid increase in pro-inflammatory cytokines and fibrogenic gene expression was also observed. In vivo chromatin immunoprecipitation assays revealed novel direct targets of HIF signaling that may contribute to hypoxia-mediated steatosis and inflammation. These data suggest that HIF-2α is a critical mediator in progression from clinically manageable steatosis to more severe steatohepatitis and liver cancer, and may be a potential therapeutic target.

OBJECTIVE

Bile acids (BA) participate in the maintenance of metabolic homeostasis acting through different signaling pathways. The nuclear BA receptor farnesoid X receptor (FXR) regulates pathways in BA, lipid, glucose, and energy metabolism, which become dysregulated in obesity. However, the role of FXR in obesity and associated complications, such as dyslipidemia and insulin resistance, has not been directly assessed.

RESEARCH DESIGN AND METHODS

Here, we evaluate the consequences of FXR deficiency on body weight development, lipid metabolism, and insulin resistance in murine models of genetic and diet-induced obesity.

RESULTS

FXR deficiency attenuated body weight gain and reduced adipose tissue mass in both models. Surprisingly, glucose homeostasis improved as a result of an enhanced glucose clearance and adipose tissue insulin sensitivity. In contrast, hepatic insulin sensitivity did not change, and liver steatosis aggravated as a result of the repression of β-oxidation genes. In agreement, liver-specific FXR deficiency did not protect from diet-induced obesity and insulin resistance, indicating a role for nonhepatic FXR in the control of glucose homeostasis in obesity. Decreasing elevated plasma BA concentrations in obese FXR-deficient mice by administration of the BA sequestrant colesevelam improved glucose homeostasis in a FXR-dependent manner, indicating that the observed improvements by FXR deficiency are not a result of indirect effects of altered BA metabolism.

CONCLUSIONS

Overall, FXR deficiency in obesity beneficially affects body weight development and glucose homeostasis.

Background

New therapies are necessary to address inadequate asthma control in many patients. This study set out to investigate whether Hypoxia Inducible Factor (HIF) is essential for development of allergic airway inflammation (AAI) and therefore a potential novel target for asthma treatment.

Methods

Mice conditionally knocked out for HIF-1β were examined for their ability to mount an allergic inflammatory response in the lung after intratracheal exposure to ovalbumin. The effects of treating wild-type mice with either ethyl-3,4-dihydroxybenzoate (EDHB) or 2-methoxyestradiol (2ME), which upregulate and downregulate HIF, respectively, were determined. HIF-1α levels were also measured in endobronchial biopsies and bronchial fluid of asthma patients and nasal fluid of rhinitis patients after challenge.

Results

Deletion of HIF-1β resulted in diminished AAI and diminished production of ovalbumin-specific IgE and IgG1. EDHB enhanced the inflammatory response, which was muted upon simultaneous inhibition of Vascular Endothelial Growth Factor (VEGF). EDHB and 2ME antagonized each other with regard to their effects on airway inflammation and mucus production. The levels of HIF-1α and VEGF increased in lung tissue and bronchial fluid of asthma patients and in the nasal fluid of rhinitis patients after challenge.

Conclusions

Our results support the notion that HIF is directly involved in the development of AAI. Most importantly, we demonstrate for the first time that HIF-1α is increased after challenge in asthma and rhinitis patients. Therefore we propose that HIF may be a potential therapeutic target for asthma and possibly for other inflammatory diseases.

Objective

Bile acids (BA) participate in the maintenance of metabolic homeostasis acting through different signaling pathways. The nuclear BA receptor farnesoid X receptor (FXR) regulates pathways in BA, lipid, glucose and energy metabolism which become dysregulated in obesity. However, the role of FXR in obesity and associated complications, such as dyslipidemia and insulin resistance, has not been directly assessed.

Research Design and Methods

Here, we evaluate the consequences of FXR-deficiency on body weight development, lipid metabolism and insulin resistance in murine models of genetic and diet-induced obesity.

Results

FXR-deficiency attenuated body weight gain and reduced adipose tissue mass in both models. Surprisingly, glucose homeostasis improved due to an enhanced glucose clearance and adipose tissue insulin sensitivity. In contrast, hepatic insulin sensitivity did not change, and liver steatosis aggravated due to the repression of β-oxidation genes. In agreement, liver-specific FXR-deficiency did not protect from diet-induced obesity and insulin resistance indicating a role for non-hepatic FXR in the control of glucose homeostasis in obesity. Decreasing elevated plasma BA concentrations in obese FXR-deficient mice by administration of the BA sequestrant colesevelam improved glucose homeostasis in a FXR-dependent manner indicating that the observed improvements by FXR-deficiency are not due to indirect effects of altered BA metabolism.

Conclusions

Overall, FXR-deficiency in obesity beneficially affects body weight development and glucose homeostasis.

Dibutylphthalate (DBP), di(2-ethylhexyl)phthalate (DEHP), and di(2-ethylhexyl)adipate (DEHA) are used as plasticizers. Their metabolites activate peroxisome proliferator-activated receptor (PPAR) α, which may be related to their toxicities. However, species differences in the receptor functions between rodents and human make it difficult to precisely extrapolate their toxicity from animal studies to human. In this paper, we compared the species differences in the activation of mouse and human hepatic PPARα by these plasticizers using wild-type (mPPARα) and humanized PPARα (hPPARα) mice. At 12 weeks old, each genotyped male mouse was classified into three groups, and fed daily for 2 weeks per os with corn oil (vehicle control), 2.5 or 5.0 mmol/kg DBP (696, 1392 mg/kg), DEHP (977, 1953 mg/kg), and DEHA (926, 1853 mg/kg), respectively. Generally, hepatic PPARα of mPPARα mice was more strongly activated than that of hPPARα mice when several target genes involving β-oxidation of fatty acids were evaluated. Interestingly, all plasticizers also activated hepatic constitutive androstane receptor (CAR) more in hPPARα mice than in mPPARα mice. Taken together, these plasticizers activated mouse and human hepatic PPARα as well as CAR. The activation of PPARα was stronger in mPPARα mice than in hPPARα mice, while the opposite was true of CAR.

Background & Aims

Iron deficiency and iron overload affect over a billion people, worldwide. Dietary iron absorption in the small intestine is required for systemic iron homeostasis. Ferroportin (FPN) is the only characterized, mammalian, basolateral iron exporter. Despite the importance of FPN in maintaining iron homeostasis, its in vivo mechanisms of regulation are unclear.

Methods

Systemic iron homeostasis was assessed in mice with intestine-specific disruption of genes encoding the von Hippel-Lindau tumor suppressor protein (Vhl), hypoxia-inducible factor (HIF)-1α, HIF-2α, and aryl hydrocarbon nuclear translocator (ARNT).

Results

We observed biphasic regulation of Fpn during iron deficiency. Fpn was rapidly induced under conditions of low iron, which required the transcription factor HIF-2α. Targeted disruption of HIF-2α in the intestine inhibited Fpn induction in mice with low iron, through loss of transcriptional activation. Analysis of the Fpn promoter and in vivo chromatin immunoprecipitation assays demonstrated that HIF-2α directly binds to the Fpn promoter and induces its expression, indicating a mechanism of transcriptional regulation of Fpn following changes in systemic levels of iron. During chronic iron deficiency, FPN protein levels also increased, via increased stability through a HIF-2α-independent pathway.

Conclusion

In mice, expression of the gene that encodes Fpn and its protein levels are regulated by distinct pathways to provide a rapid and sustained response to acute and chronic iron deficiency. Therapies that target FPN might be developed for patients with iron-related disorders..

Hepatocyte nuclear factor 4α (HNF4α) and CCAAT/enhancer-binding protein α (C/EBPα) are important for the transcriptional control of coagulation factors. To determine in vivo the direct role of HNF4α and C/EBPα in control of genes encoding coagulation factors, a synthetic small interfering (si)RNA approach was used that enabled strong reduction of mouse hepatic HNF4α and C/EBPα under conditions that minimized target-related secondary effects. For both HNF4α and C/EBPα, intravenous injection of specific synthetic siRNAs (siHNF4α and siC/EBPα) resulted in more than 75% reduction in their liver transcript and protein levels 2 days post-injection. For siHNF4α, this coincided with marked and significantly reduced transcript levels of the coagulation genes Hrg, Proz, Serpina5, F11, F12, F13b, Serpinf2, F5, and F9 (in order of magnitude of effect) as compared to levels in control siRNA injected animals. Significant decreases in HNF4α target gene mRNA levels were also observed at 5 days post-siRNA injection, despite a limited level of HNF4α knockdown at this time point. Compared to HNF4α, C/EBPα knockdown had a modest impact on genes encoding coagulation factors. A strong reduction in C/EBPα transcript and protein levels resulted in significantly affected transcript levels of the control genes Pck1 and Fasn and a modest downregulation for coagulation genes Fba, Fbg and F5. F5 and F11 were the sole coagulation genes that were significantly affected upon prolonged (5 day) C/EBPα knockdown. We conclude that in the mouse, HNF4α has a direct and essential regulatory role for multiple hepatic coagulation genes, while a role for C/EBPα is more restricted. In addition, this study demonstrates that synthetic siRNA provides a simple and fast means for determining liver transcription factor involvement in vivo.

Sulfatides are one of the major sphingoglycolipids in mammalian serum and are synthesized and secreted mainly from the liver as a component of lipoproteins. Recent studies revealed a protective role for serum sulfatides against arteriosclerosis and hypercoagulation. Although peroxisome proliferator-activated receptor (PPAR) α has important functions in hepatic lipoprotein metabolism, its association with sulfatides has not been investigated. In this study, sulfatide levels and the expression of enzymes related to sulfatide metabolism were examined using wild-type (+/+), Ppara-heterozygous (+/−), and Ppara-null (−/−) mice given a control diet or one containing 0.1% fenofibrate, a clinically used hypolipidemic drug and PPARα activator. Fenofibrate treatment increased serum and hepatic sulfatides in Ppara (+/+) and (+/−) mice through a marked induction of hepatic cerebroside sulfotransferase (CST), a key enzyme in sulfatide synthesis, in a PPARα-dependent manner. Furthermore, increases in CST mRNA levels were correlated with mRNA elevations of several known PPARα target genes, and such changes were not observed for other sulfatide-metabolism enzymes in the liver. These results suggest that PPARα activation enhances hepatic sulfatide synthesis via CST induction and implicate CST as a novel PPARα target gene.

Lithocholic acid (LCA) is an endogenous compound associated with hepatic toxicity during cholestasis. LCA exposure in mice resulted in decreased serum lysophosphatidylcholine (LPC) and sphingomyelin levels due to elevated lysophosphatidylcholine acyltransferase (LPCAT) and sphingomyelin phosphodiesterase (SMPD) expression. Global metabolome analysis indicated significant decreases in serum palmitoyl-, stearoyl-, oleoyl- and linoleoyl-LPC levels after LCA exposure. LCA treatment also resulted in decreased serum sphingomyelin levels and increased hepatic ceramide levels, and induction of LPCAT and SMPD mRNAs. Transforming growth factor-β TGF-β) induced Lpcat2/4 and Smpd3 gene expression in primary hepatocytes and the induction was diminished by pretreatment with the SMAD3 inhibitor SIS3. Furthermore, alteration of the LPC metabolites and Lpcat1/2/4 and Smpd3 expression was attenuated in LCA-treated farnesoid X receptor-null mice that are resistant to LCA-induced intrahepatic cholestasis. This study revealed that LCA induced disruption of phospholipid/sphingolipid homeostasis through TGF-β signaling and that serum LPC is a biomarker for biliary injury.

Radiation metabolomics has aided in the identification of a number of biomarkers in cells and mice by ultra-performance liquid chromatography-coupled time-of-flight mass spectrometry (UPLC-ESI-QTOFMS) and in rats by gas chromatography-coupled mass spectrometry (GCMS). These markers have been shown to be both dose- and time-dependent. Here UPLC-ESI-QTOFMS was used to analyze rat urine samples taken from 12 rats over 7 days; they were either sham-irradiated or γ-irradiated with 3 Gy after 4 days of metabolic cage acclimatization. Using multivariate data analysis, nine urinary biomarkers of γ radiation in rats were identified, including a novel mammalian metabolite, N-acetyltaurine. These upregulated urinary biomarkers were confirmed through tandem mass spectrometry and comparisons with authentic standards. They include thymidine, 2′-deoxyuridine, 2′deoxyxanthosine, N1-acetylspermidine, N-acetylglucosamine/galactosamine-6-sulfate, N-acetyltaurine, N-hexanoylglycine, taurine and, tentatively, isethionic acid. Of these metabolites, 2′-deoxyuridine and thymidine were previously identified in the rat by GCMS (observed as uridine and thymine) and in the mouse by UPLC-ESI-QTOFMS. 2′Deoxyxanthosine, taurine and N-hexanoylglycine were also seen in the mouse by UPLC-ESI-QTOFMS. These are now unequivocal cross-species biomarkers for ionizing radiation exposure. Downregulated biomarkers were shown to be related to food deprivation and starvation mechanisms. The UPLC-ESI-QTOFMS approach has aided in the advance for finding common biomarkers of ionizing radiation exposure.