Ppara-null Mice Research Articles

PPARα suppresses low-intensity-noise-induced body weight gain in mice: the activated HPA axis plays an critical role.

As the second most risky environmental pollution, noise imposes threats to human health. Exposure to high-intensity noise causes hearing impairment, psychotic disorders, endocrine modifications. The relationship among low-intensity noise, obesity and lipid-regulating nuclear factor PPARα is not yet clear. In this study, male wild-type (WT) and Pparα-null (KO) mice on a high-fat diet (HFD) were exposed to 75 dB noise for 12 weeks to explore the effect of low-intensity noise on obesity development and the role of PPARα. 3T3-L1 cells were treated with dexamethasone (DEX) and sodium oleate (OA) to verify the down-stream effect of hypothalamic-pituitary-adrenal (HPA) axis activation on the adipose tissues. The average body weight gain (BWG) of WT mice on HFD exposed to noise was inhibited, which was not observed in KO mice. The mass and adipocyte size of adipose tissues accounted for the above difference of BWG tendency. In WT mice on HFD, the adrenocorticotropic hormone level was increased by the noise challenge. The aggravation of fatty liver by noise exposure occurred in both mouse lines, and the transport of hepatic redundant lipid to adipose tissues were similar. The lipid metabolism in adipose tissue driven by HPA axis accorded with the BWG inhibition in vivo, validated in 3T3-L1 adipogenic stem cells. Chronic exposure to low-intensity noise aggravated fatty liver in both WT and KO mice. BWG inhibition was observed only in WT mice, which covered up the aggravation of fatty liver by noise exposure. PPARα mediates the activation of HPA axis by noise exposure in mice on HFD. Elevated adrenocorticotropic hormone (ACTH) promoted lipid metabolism in adipocytes, which contributed to the disassociation of BWG and fatty liver development in male WT mice. Summary of PPARα suppresses noise-induced body weight gain in mice on high-fat-diet. Chronic exposure to low-intensity noise exposure inhibited BWG by PPARα-dependent activation of the HPA axis.

Distinct bile acid alterations in response to a single administration of PFOA and PFDA in mice

Per- and polyfluoroalkyl substances (PFASs), a group of synthetic chemicals that were once widely used for industrial purposes and in consumer products, are widely found in the environment and in human blood due to their extraordinary resistance to degradation. Once inside the body, PFASs can activate nuclear receptors such as PPARα and CAR. The present study aimed to investigate the impact of perfluorooctanoic acid (PFOA) and perfluorodecanoic acid (PFDA) on liver structure and functions, as well as bile acid homeostasis in mice. A single administration of 0.1 mmole/kg of PFDA, not PFOA, elevated serum ALT and bilirubin levels and caused cholestasis in WT mice. PFDA increased total and various bile acid species in serum but decreased them in the liver. Furthermore, in mouse livers, PFDA, not PFOA, down-regulated mRNA expression of uptake transporters (Ntcp, Oatp1a1, 1a4, 1b2, and 2b1) but induced efflux transporters (Bcrp, Mdr2, and Mrp2–4). In addition, PFDA, not PFOA, decreased Cyp7a1, 7b1, 8b1, and 27a1 mRNA expression in mouse livers with concomitant hepatic accumulation of cholesterol. In contrast, in PPARα-null mice, PFDA did not increase serum ALT, bilirubin, or total bile acids, but produced prominent hepatosteatosis; and the observed PFDA-induced expression changes of transporters and Cyps in WT mice were largely attenuated or abolished. In CAR-null mice, the observed PFDA-induced bile acid alterations in WT mice were mostly sustained. These results indicate that, at the dose employed, PFDA has more negative effects than PFOA on liver function. PPARα appears to play a major role in mediating most of PFDA-induced effects, which were absent or attenuated in PPARα-null mice. Lack of PPARα, however, exacerbated hepatic steatosis. Our findings indicate separated roles of PPARα in mediating the adaptive responses to PFDA: protective against hepatosteatosis but exacerbating cholestasis.

Oleuropein Promotes Neural Plasticity and Neuroprotection via PPARα-Dependent and Independent Pathways.

Oleuropein (OLE), a main constituent of olives, displays a pleiotropic beneficial dynamic in health and disease; the effects are based mainly on its antioxidant and hypolipidemic properties, and its capacity to protect the myocardium during ischemia. Furthermore, OLE activates the peroxisome proliferator-activated receptor (PPARα) in neurons and astrocytes, providing neuroprotection against noxious biological reactions that are induced following cerebral ischemia. The current study investigated the effect of OLE in the regulation of various neural plasticity indices, emphasizing the role of PPARα. For this purpose, 129/Sv wild-type (WT) and Pparα-null mice were treated with OLE for three weeks. The findings revealed that chronic treatment with OLE up-regulated the brain-derived neurotrophic factor (BDNF) and its receptor TrkB in the prefrontal cortex (PFC) of mice via activation of the ERK1/2, AKT and PKA/CREB signaling pathways. No similar effects were observed in the hippocampus. The OLE-induced effects on BDNF and TrkB appear to be mediated by PPARα, because no similar alterations were observed in the PFC of Pparα-null mice. Notably, OLE did not affect the neurotrophic factors NT3 and NT4/5 in both brain tissues. However, fenofibrate, a selective PPARα agonist, up-regulated BDNF and NT3 in the PFC of mice, whereas the drug induced NT4/5 in both brain sites tested. Interestingly, OLE provided neuroprotection in differentiated human SH-SY5Y cells against β-amyloid and H2O2 toxicity independently from PPARα activation. In conclusion, OLE and similar drugs, acting either as PPARα agonists or via PPARα independent mechanisms, could improve synaptic function/plasticity mainly in the PFC and to a lesser extent in the hippocampus, thus beneficially affecting cognitive functions.

Cardiomyocyte peroxisome proliferator-activated receptor α prevents septic cardiomyopathy via improving mitochondrial function.

Clinically, cardiac dysfunction is a key component of sepsis-induced multi-organ failure. Mitochondria are essential for cardiomyocyte homeostasis, as disruption of mitochondrial dynamics enhances mitophagy and apoptosis. However, therapies targeted to improve mitochondrial function in septic patients have not been explored. Transcriptomic data analysis revealed that the peroxisome proliferator-activated receptor (PPAR) signaling pathway in the heart was the most significantly decreased inthe cecal ligation puncture-treated mouse heart model, and PPARα was the most notably decreased among the three PPAR family members. Male Pparafl/fl (wild-type), cardiomyocyte-specific Ppara-deficient (PparaΔCM), and myeloid-specific Ppara-deficient (PparaΔMac) mice were injected intraperitoneally with lipopolysaccharide (LPS) to induce endotoxic cardiac dysfunction. PPARα signaling was decreased in LPS-treated wild-type mouse hearts. To determine the cell type in which PPARα signaling was suppressed, the cell type-specific Ppara-null mice were examined. Cardiomyocyte- but not myeloid-specific Ppara deficiency resulted in exacerbated LPS-induced cardiac dysfunction. Ppara disruption in cardiomyocytes augmented mitochondrial dysfunction, as revealed by damaged mitochondria, lowered ATP contents, decreased mitochondrial complex activities, and increased DRP1/MFN1 protein levels. RNA sequencing results further showed that cardiomyocyte Ppara deficiency potentiated the impairment of fatty acid metabolism in LPS-treated heart tissue. Disruption of mitochondrial dynamics resulted in increased mitophagy and mitochondrial-dependent apoptosis in Ppara△CM mice. Moreover, mitochondrial dysfunction caused an increase of reactive oxygen species, leading to increased IL-6/STAT3/NF-κB signaling. 3-Methyladenine (3-MA, an autophagosome formation inhibitor) alleviated cardiomyocyte Ppara disruption-induced mitochondrial dysfunction and cardiomyopathy. Finally, pre-treatment with the PPARα agonist WY14643 lowered mitochondrial dysfunction-induced cardiomyopathy in hearts from LPS-treated mice. Thus, cardiomyocyte but not myeloid PPARα protects against septic cardiomyopathy by improving fatty acid metabolism and mitochondrial dysfunction, thus highlighting that cardiomyocyte PPARα may be a therapeutic target for the treatment of cardiac disease.

Metabolomics Reveals Gut Microbiota Contribute to PPARα Deficiency-Induced Alcoholic Liver Injury.

Incidence and mortality rates of alcoholic liver disease (ALD) is one of the highest in the world. In the present study, we found that the genetic knockout nuclear receptor the peroxisome proliferator-activated receptor α (PPARα) exacerbated ALD. Lipidomics of the liver revealed changed levels of lipid species encompassing phospholipids, ceramides (CM), and long-chain fatty acids in Ppara-null mice induced by ethanol. Moreover, 4-hydroxyphenylacetic acid (4-HPA) was changed as induced by ethanol in the metabolome of urine. Moreover, the phylum level analysis showed a decrease in the level of Bacteroidetes and an increase in the level of Firmicutes after alcohol feeding in Ppara-null mice, while there was no change in wild-type mice. In Ppara-null mice, the level of Clostridium_sensu_stricto_1 and Romboutsia were upregulated after alcohol feeding. These data revealed that PPARα deficiency potentiated alcohol-induced liver injury through promotion of lipid accumulation, changing the metabolome of urine, and increasing the level of Clostridium_sensu_stricto_1 and Romboutsia. 4-HPA could improve ALD in mice by regulating inflammation and lipid metabolism. Therefore, our findings suggest a novel approach to the treatment of ALD: focusing on the gut microbiota and its metabolites. Data are available via ProteomeXchange (PXD 041465).

Keratin 79 is a PPARA target that is highly expressed by liver damage

Keratins are key structural proteins found in skin and other epithelial tissues. Keratins also protect epithelial cells from damage or stress. Fifty-four human keratins were identified and classified into two families, type I and type II. Accumulating studies showed that keratin expression is highly tissue-specific and used as a diagnostic marker for human diseases. Notably, keratin 79 (KRT79) is type II cytokeratin that was identified as regulator of hair canal morphogenesis and regeneration in skin, but its role in liver remains unclear. KRT79 is undetectable in normal mouse but its expression is significantly increased by the PPARA agonist WY-14643 and fenofibrate, and completely abolished in Ppara-null mice. The Krt79 gene has functional PPARA binding element between exon 1 and exon 2. Hepatic Krt79 is regulated by HNF4A and HER2. Moreover, hepatic KRT79 is also significantly elevated by fasting- and high-fat diet-induced stress, and these increases are completely abolished in Ppara-null mice. These findings suggest that hepatic KRT79 is controlled by PPARA and is highly associated with liver damage. Thus, KRT79 may be considered as a diagnostic marker for human liver diseases.

PPARα is involved in high-fat diet-induced risk avoidance impairment via the regulation of hippocampal BDNF.

Risk avoidance behaviors are essential for survival. "Uncontrollable" risk-taking behaviors in animals or humans may have severe adverse consequences. In humans, a large proportion of psychiatric disorders are accompanied by impairments in risk avoidance. Obesity is associated with psychiatric disorders. Peroxisome proliferator-activated receptor α (PPARα) takes part in regulating lipid metabolism and neuronal function. Here, we investigated the effect of high-fat diet (HFD)-induced obesity on risk avoidance and the role of PPARα in this behavior. Male PPARα-null (KO) mice and wild-type (WT) mice were assigned to four different groups: WT-CON and KO-CON (normal diet); WT-HFD and KO-HFD (high fat diet). The HFD began at week 6 and was continued until sampling. A series of behavioral tests were performed at week 11. We found that WT but not KO mice fed with a HFD exhibited weight gain and risk avoidance impairment, compared with the mice fed with a normal diet. The staining of c-Fos revealed that the hippocampus was the main brain region involved in risk avoidance behavior. Moreover, biochemical analysis suggested that the decreased levels of the brain-derived neurotrophic factor (BDNF) in the hippocampus might contribute to risk avoidance impairment induced by a HFD. These results indicated that PPARα is involved in HFD-induced risk avoidance impairment via the regulation of hippocampal BDNF.

Down-regulation of hepatic CLOCK by PPARα is involved in inhibition of NAFLD.

This work aimed to investigate the role of nuclear factor peroxisome proliferator-activated receptor α (PPARα) in modification of circadian clock and their relevance to development of nonalcoholic fatty liver disease (NAFLD). Both male wild-type (WT) and Pparα-null (KO) mice treated with high-fat diet (HFD) were used to explore the effect of PPARα and lipid diet on the circadian rhythm. WT, KO, and PPARα-humanized (hPPARα) mice were treated with PPARα agonist fenofibrate to reveal the hPPARα dependence of circadian locomotor output cycles kaput (CLOCK) down-regulation. The mouse model and hepatocyte experiments were designed to verify the action of PPARα in down-regulating CLOCK and lipid accumulation in vivo and in vitro. Strongest NAFLD developed in mice fed 45%HFD, and it was inhibited in WT mice. The activity rhythm of WT mice was found to be different from that of the KO mice on normal diet and HFD. The core circadian factor CLOCK was down-regulated by HFD in both WT and KO mice in the liver, not in the hypothalamus. More interestingly, hepatic CLOCK was down-regulated by basal PPARα and activated PPARα in dose dependence of fenofibrate. Accordingly, CLOCK down-regulation dependent of PPARα activity was involved in inhibition of lipid metabolism in hepatocytes. Down-regulation of hepatic CLOCK by basal PPARα contributes to tolerance against development of NAFLD. Inhibition of CLOCK by activated PPARα is involved in inhibition of NAFLD by PPARα agonists. KEY MESSAGES: •PPARα inhibited NAFLD development induced by HFD. •PPARα mediated modifications of circadian rhythm and the hepatic circadian factor CLOCK in NAFLD models. •Down-regulation of hepatic CLOCK by basal PPARα contributed to tolerance against development of NAFLD. •Inhibition of CLOCK by activated PPARα was involved in therapeutic actions against fatty liver diseases by PPARα agonists.

Physical exercise regulates apoptosis and prostatic inflammatory effects induced by high-fat diet in PPAR-alpha deleted mice

The high-fat diet (HFD) promotes obesity and develops inflammation, causing dysregulation of energy metabolism and prostatic neoplastic tissue changes. PPARɑ deletion leads to loss of homeostasis between the pro and anti-inflammatory response, and dysregulation of lipid metabolism, causing changes in different physiological processes and damage to the prostate. On the other hand, aerobic physical exercise has been suggested as a non-pharmacological tool to improve energy metabolism and cellular metabolism in the prostate, however, the underlying molecular mechanism remains unclear. the current study aimed to evaluate PPARα as a possible regulator of the protective effects of aerobic physical exercise in the prostate by examining prostatic alterations in wild-type and PPARα deletion mice fed a standard diet or an HFD. Wild-type and PPARα-null mice were fed a standard or HFD diet for 12 weeks, and submitted to aerobic physical exercise for 8 weeks. The HFD promoted the increase of inflammatory markers IL-6, TNF-α, NF-kB, and an increase of inflammatory foci in animals in both genotypes. Although the PPARα deletion animals submitted to the aerobic physical exercise were not able to regulate response pro-inflammatory, but promoted an increase in IL-10 in the prostate. In animals WT, the aerobic physical exercise, reduced all inflammatory markers, improve the inflammatory response, and showed a higher expression of BAX and IL-10 proteins was protective against prostatic tissue lesions. Suggested that PPARα deletion associated with HFD suppressed apoptosis and increased damage prostate. On other hand, aerobic physical exercise improves prostatic tissue by increasing the response to anti-inflammatory and apoptosis protein.

Crosstalk between CYP2E1 and PPARα substrates and agonists modulate adipose browning and obesity

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 (PPARα) 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 PPARα agonists, thus explaining how CYP2E1 deficiency causes hepatic PPARα activation through increasing cellular levels of endogenous PPARα agonists. Translationally, a CYP2E1 inhibitor was found to activate the PPARα–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 PPARα 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.

Metabolomics reveals the role of PPARα in Tripterygium Wilfordii-induced liver injury

Ethnopharmacological relevanceTripterygium glycosides tablets (TGT) and Tripterygium wilfordii tablets (TWT) have been used to treat autoimmune diseases clinically, however, the side effects of TWT are higher than TGT, especially for hepatotoxicity. The aim of the studyThis study aims to determine the mechanism of TWT-induced liver injury. Materials and methodsWe performed metabolomic analysis of samples from mice with liver injury induced by TGT and TWT. Ppara-null mice were used to determine the role of PPARα in TWT-induced liver injury. ResultsThe results indicated that TWT induced the accumulation of medium- and long-chain carnitines metabolism, which was associated with the disruption of PPARα-IL6-STAT3 axis. PPARα agonists fenofibrate could reverse the liver injury from TWT and TP/Cel, and its protective role could be attenuated in Ppara-null mice. The toxicity difference of TWT and TGT was due to the different ratio of triptolide (TP) and celastrol (Cel) in the tablet in which TP/Cel was lower in TWT than TGT. The hepatotoxicity induced by TP and Cel also inhibited PPARα and upregulated IL6-STAT3 axis, which could be alleviated following by PPARα activation. ConclusionsThese results indicated that PPARα plays an important role in the hepatotoxicity of Tripterygium wilfordii, and PPARα activation may offer a promising approach to prevent hepatotoxicity induced by the preparations of Tripterygium wilfordii.

Oleamide, a Sleep-Inducing Supplement, Upregulates Doublecortin in Hippocampal Progenitor Cells via PPARα.

Doublecortin (DCX), a microtubule associated protein, has emerged as a central biomarker of hippocampal neurogenesis. However, molecular mechanisms by which DCX is regulated are poorly understood. Since sleep is involved with the acquisition of memory and oleamide or 9-Octadecenamide (OCT) is a sleep-inducing supplement in human, we examined whether OCT could upregulate DCX in hippocampal progenitor cells (HPCs). We employed real-time PCR, western blot, immunostaining, chromatin immunoprecipitation, lentiviral transduction in HPCs, and the calcium influx assay. OCT directly upregulated the transcription of Dcx in HPCs via activation of peroxisome proliferator-activated receptor α (PPARα), a lipid-lowering transcription factor. We observed that, HPCs of Ppara-null mice displayed significant impairment in DCX expression and neuronal differentiation as compared to that of wild-type mice. Interestingly, treatment with OCT stimulated the differentiation process of HPCs in wild-type, but not Ppara-null mice. Reconstruction of PPARα in mouse Ppara-null HPCs restored the expression of DCX, which was further stimulated with OCT treatment. In contrast, a dominant-negative mutant of PPARα significantly attenuated the stimulatory effect of OCT on DCX expression and suppressed neuronal differentiation of human neural progenitor cells. Furthermore, RNA microarray, STRING, chromatin immunoprecipitation, site-directed mutagenesis, and promoter reporter assay have identified DCX as a new target of PPARα. These results indicate that OCT, a sleep supplement, directly controls the expression of DCX and suggest that OCT may be repurposed for stimulating the hippocampal neurogenesis.

The role of mouse and human peroxisome proliferator-activated receptor-α in modulating the hepatic effects of perfluorooctane sulfonate in mice

Perfluorooctane sulfonate (PFOS) is a stable environmental contaminant that can activate peroxisome proliferator-activated receptor alpha (PPARα). In the present work, the specific role of mouse and human PPARα in mediating the hepatic effects of PFOS was examined in short-term studies using wild type, Ppara-null and PPARA-humanized mice. Mice fed 0.006 % PFOS for seven days (∼10 mg/kg/day), or 0.003 % PFOS for twenty-eight days (∼5 mg/kg/day), exhibited higher liver and serum PFOS concentrations compared to controls. Relative liver weights were also higher following exposure to dietary PFOS in all three genotypes as compared vehicle fed control groups. Histopathological examination of liver sections from mice treated for twenty-eight days with 0.003 % PFOS revealed a phenotype consistent with peroxisome proliferation, in wild-type and PPARA-humanized mice that was not observed in Ppara-null mice. With both exposures, expression of the PPARα target genes, Acox1, Cyp4a10, was significantly increased in wild type mice but not in Ppara-null or PPARA-humanized mice. By contrast, expression of the constitutive androstane receptor (CAR) target gene, Cyp2b10, and the pregnane X receptor (PXR) target gene, Cyp3a11, were higher in response to PFOS administration in all three genotypes compared to controls for both exposure periods. These results indicate that mouse PPARα can be activated in the liver by PFOS causing increased expression of Acox1, Cyp4a10 and histopathological changes in the liver. While histopathological analyses indicated the presence of mouse PPARα-dependent hepatic peroxisome proliferation in wild-type (a response associated with activation of PPARα) and a similar phenotype in PPARA-humanized mice, the lack of increased Acox1 and Cyp4a10 mRNA by PFOS in PPARA-humanized mice indicates that the human PPARα was not as responsive to PFOS as mouse PPARα with this dose regimen. Moreover, results indicate that hepatomegaly caused by PFOS does not require mouse or human PPARα and could be due to effects induced by activation of CAR and/or PXR.

Perfluorooctanoic acid induces liver and serum dyslipidemia in humanized PPARα mice fed an American diet

Per- and polyfluoroalkyl substances (PFAS) are pervasive in the environment resulting in nearly universal detection in people. Human serum PFAS concentrations are strongly associated with increased serum low-density lipoprotein cholesterol (LDL-C), and growing evidence suggests an association with serum triacylglycerides (TG). Here, we tested the hypothesis that perfluorooctanoic acid (PFOA) dysregulates liver and serum triacylglycerides in human peroxisome proliferator activated receptor α (hPPARα)-expressing mice fed an American diet. Mice were exposed to PFOA (3.5 mg/L) in drinking water for 6 weeks resulting in a serum concentration of 48 ± 9 μg/ml. In male and female hPPARα mice, PFOA increased total liver TG and TG substituted with saturated and monounsaturated fatty acids. Lack of expression of PPARα alone also increased total liver TG, and PFOA treatment had little effect on liver TG in PPARα null mice. In hPPARα mice, PFOA neither significantly increased nor decreased serum TG; however, there was a modest increase in TG associated with very low-density cholesterol particles in both sexes. Intriguingly, in female PPARα null mice, PFOA significantly increased serum TG, with a similar trend in males. PFOA also modified fatty acid and TG homeostasis-related gene expression in liver, in a hPPARα-dependent manner, but not in adipose. The results of our study and others reveal the importance of context (serum concentration and genotype) in determining the effect of PFOA on lipid homeostasis.

Oleuropein-Induced Acceleration of Cytochrome P450-Catalyzed Drug Metabolism: Central Role for Nuclear Receptor Peroxisome Proliferator-Activated Receptor α.

Oleuropein (OLE), the main constituent of Olea europaea, displays pleiotropic beneficial effects in health and disease, which are mainly attributed to its anti-inflammatory and cardioprotective properties. Several food supplements and herbal medicines contain OLE and are available without a prescription. This study investigated the effects of OLE on the main cytochrome P450s (P450s) catalyzing the metabolism of many prescribed drugs. Emphasis was given to the role of peroxisome proliferator-activated receptor α (PPARα), a nuclear transcription factor regulating numerous genes including P450s. 129/Sv wild-type and Ppara-null mice were treated with OLE for 6 weeks. OLE induced Cyp1a1, Cyp1a2, Cyp1b1, Cyp3a14, Cyp3a25, Cyp2c29, Cyp2c44, Cyp2d22, and Cyp2e1 mRNAs in liver of wild-type mice, whereas no similar effects were observed in Ppara-null mice, indicating that the OLE-induced effect on these P450s is mediated by PPARα. Activation of the pathways related to phosphoinositide 3-kinase/protein kinase B (AKT)/forkhead box protein O1, c-Jun N-terminal kinase, AKT/p70, and extracellular signal-regulated kinase participates in P450 induction by OLE. These data indicate that consumption of herbal medicines and food supplements containing OLE could accelerate the metabolism of drug substrates of the above-mentioned P450s, thus reducing their efficacy and the outcome of pharmacotherapy. Therefore, OLE-induced activation of PPARα could modify the effects of drugs due to their increased metabolism and clearance, which should be taken into account when consuming OLE-containing products with certain drugs, in particular those of narrow therapeutic window. SIGNIFICANCE STATEMENT: This study indicated that oleuropein, which belongs to the main constituents of the leaves and olive drupes of Olea europaea, induces the synthesis of the major cytochrome P450s (P450s) metabolizing the majority of prescribed drugs via activation of peroxisome proliferator-activated receptor α. This effect could modify the pharmacokinetic profile of co-administered drug substrates of the P450s, thus altering their therapeutic efficacy and toxicity.

Diminished Hepatocarcinogenesis by a Potent, High-Affinity Human PPARα Agonist in PPARA-Humanized Mice.

Ppara-null and PPARA-humanized mice are refractory to hepatocarcinogenesis caused by the peroxisome proliferator-activated receptor-α (PPARα) agonist Wy-14,643. However, the duration of these earlier studies was limited to approximately 1 year of treatment, and the ligand used has a higher affinity for the mouse PPARα compared to the human PPARα. Thus, the present study examined the effect of long-term administration of a potent, high-affinity human PPARα agonist (GW7647) on hepatocarcinogenesis in wild-type, Ppara-null, or PPARA-humanized mice. In wild-type mice, GW7647 caused hepatic expression of known PPARα target genes, hepatomegaly, hepatic MYC expression, hepatic cytotoxicity, and a high incidence of hepatocarcinogenesis. By contrast, these effects were essentially absent in Ppara-null mice or diminished in PPARA-humanized mice, although hepatocarcinogenesis was observed in both genotypes. Enhanced fatty change (steatosis) was also observed in both Ppara-null and PPARA-humanized mice independent of GW7647. PPARA-humanized mice administered GW7647 also exhibited increased necrosis after 5 weeks of treatment. Results from these studies demonstrate that the mouse PPARα is required for hepatocarcinogenesis induced by GW7647 administered throughout adulthood. Results also indicate that a species difference exists between rodents and human PPARα in the response to ligand activation of PPARα. The hepatocarcinogenesis observed in control and treated Ppara-null mice is likely mediated in part by increased hepatic fatty change, whereas the hepatocarcinogenesis observed in PPARA-humanized mice may also be due to enhanced fatty change and cytotoxicity that could be influenced by the minimal activity of the human PPARα in this mouse line on downstream mouse PPARα target genes. The Ppara-null and PPARA-humanized mouse models are valuable tools for examining the mechanisms of PPARα-induced hepatocarcinogenesis, but the background level of liver cancer must be controlled for in the design and interpretation of studies that use these mice.

Regulation of hepatic transcriptional architecture by Pparα and fatty acid oxidation

Hepatic lipid biology is a central regulator of metabolic physiology, requiring tight coordination between the hepatocyte's metabolic state and transcriptional output. Peroxisome proliferator-activated receptor alpha (Pparα) plays a key role in this process as a master regulator of oxidative gene expression. To better resolve Pparα's role in the hepatic response to acutely elevated fatty acids, Pparα-null mice were crossed to mice harboring a liver-specific knockout of carnitine palmitoyltransferase 2 (Cpt2), an obligate enzyme for mitochondrial β-oxidation. The oxidation deficit leads to drastic fatty acid accumulation following a 24hr fast, providing a handle by which to investigate Pparα's response to excess fatty acids. RNA-seq on fasted WT, Cpt2L-/-, Ppar⍺-/-, and Cpt2L-/-;Ppar⍺-/- liver uncovered two distinct classes of Pparα-influenced gene expression: those wholly dependent upon Pparα, such as Fgf21 and Hmgcs2, and those with partial independence, such as Acot2 and Pdk4. The latter implies a secondary regulatory mechanism for a subset of canonical Pparα target genes. Complementing this hypothesis, ATAC-seq demonstrates genes with partial Ppar⍺ independence retain promotor accessibility in Cpt2L-/-;Ppar⍺-/-, but not Ppar⍺-/-, mice, whereas genes wholly dependent on Ppar⍺ display significantly reduced promotor accessibility in both Ppar⍺-null genotypes. Co-analysis of ATAC-seq and ChIP-seq for H3K4me1 and H3K27ac indicates that genes wholly dependent on Pparα are more closely associated with poised distal enhancer elements, and those with partial Pparα independence show active albeit blunted enhancer activity. H3K4me1 occupancy suggests that Pparα target genes are primed regardless of Pparα expression. Taken together, these data provide evidence of a Pparα-independent genomic control mechanism that acts in parallel with Pparα signaling to promote transcription of canonical Pparα target genes.

Fenofibrate reverses liver fibrosis in cholestatic mice induced by alpha-naphthylisothiocyanate.

Cholestatic liver fibrosis occurs in liver injuries accompanied by inflammation, which develops into cirrhosis if not effectively treated in early stage. The aim of the study is to explore the effect of fenofibrate on liver fibrosis in chronic cholestatic mice. In this study, wild-type (WT) and Pparα-null (KO) mice were dosed alpha-naphthylisothiocyanate (ANIT) diet to induce chronic cholestasis. Induced liver fibrosis was determined by pathological biomarkers. Then fenofibrate 25 mg/kg was orally administrated to mice twice/day for 14 days. Serum and liver samples were collected for analysis of biochemistry and fibrosis. In WT mice, cholestatic biomarkers were increased by 5-8-fold and the expression of tissue inhibitors of metalloproteinases 1 (TIMP-1), Monocyte chemoattractant protein 1 (MCP-1), Collagen protein I (Collagen I) was increased by more than 10-fold. Fenofibrate significantly downgraded the biochemical and fibrotic biomarkers. In Western blot analysis, levels of collagenI and alpha-smooth muscle actin (α-SMA) were strongly inhibited by fenofibrate. In KO mice, liver fibrosis was induced successfully, but no improvement after fenofibrate treatment was observed. These data showed low-dose fenofibrate reverses cholestatic liver fibrosis in WT mice but not in KO mice, suggesting the dependence of therapeutic action on peroxisome proliferator-activated receptor alpha (PPARα). The study offers an additional therapeutic strategy for cholestatic liver fibrosis in practice.

PPARα/RXRα downregulates amino acid catabolism in the liver via interaction with HNF4α promoting its proteasomal degradation

The preservation of body proteins is essential to guarantee their functions in organisms. Therefore, the utilization of amino acids as energy substrates is regulated by a precise fine-tuned mechanism. Recent evidence suggests that the transcription factors peroxisome proliferator-activated receptor alpha (PPARα) and hepatocyte nuclear factor 4 alpha (HNF4α) are involved in this regulatory mechanism. Thus, the aim of this study was to determine how these transcription factors interact to regulate the expression of amino acid catabolism genes. In vivo studies using PPARα-knockout mice (Pparα-null) fed different amounts of dietary protein showed that in the absence of PPARα, there was a significant increase in HNF4α abundance in the liver, which corresponded with an increase in amino acid catabolizing enzyme (AACE) expression and the generation of increased amounts of postprandial urea. Moreover, this effect was proportional to the increase in dietary protein consumed. Chromatin immunoprecipitation assays showed that HNF4α can bind to the promoter of AACE serine dehydratase (SDS), an effect that was potentiated by dietary protein in the Pparα-null mice. The mechanistic studies revealed that the presence of retinoid X receptor alpha (RXRα) is essential to repress HNF4α activity in the presence of PPARα, and this interaction accelerates HNF4α degradation via the proteasome pathway. These results showed that PPARα can downregulate liver amino acid catabolism in the presence of RXRα by inhibiting HNF4α activity.

Perfluorooctanoic acid activates multiple nuclear receptor pathways and skews expression of genes regulating cholesterol homeostasis in liver of humanized PPARα mice fed an American diet

Humans are exposed to per- and polyfluoroalkyl substances (PFAS) in their drinking water, food, air, dust, and by direct use of consumer products. Increased concentrations of serum total cholesterol and low density lipoprotein cholesterol are among the endpoints best supported by epidemiology. The objectives of this study were to generate a new model for examining PFAS-induced dyslipidemia and to conduct molecular studies to better define mechanism(s) of action. We tested the hypothesis that perfluorooctanoic acid (PFOA) exposure at a human-relevant level dysregulates expression of genes controlling cholesterol homeostasis in livers of mice expressing human PPARα (hPPARα). Female and male hPPARα and PPARα null mice were fed a diet based on the “What we eat in America” analysis and exposed to PFOA in drinking water (8 μM) for 6 weeks. This resulted in a serum PFOA concentration of 48 μg/ml. PFOA increased liver mass, which was associated with histologically-evident lipid accumulation. Pooled analyses of serum lipoprotein cholesterol suggest that PFOA increased serum cholesterol, particularly in male mice. PFOA induced PPARα and constitutive androstane receptor target gene expression in liver. Expression of genes in four pathways regulating cholesterol homeostasis were also measured. PFOA decreased expression of Hmgcr in a PPARα-dependent manner. PFOA decreased expression of Ldlr and Cyp7a1 in a PPARα-independent manner. Apob expression was not changed. Sex differences were evident. This novel study design (hPPARα mice, American diet, long term exposure) generated new insight on the effects of PFOA on cholesterol regulation in the liver and the role of hPPARα.