PPARα Knockout Mice Research Articles

PPARα modulates the TSH β‐subunit mRNA expression in thyrotrope TαT1 cells and in a mouse model

Fasting leads to a significant downregulation of the hypothalamus-pituitary-thyroid axis, and peroxisome proliferator-activated receptor (PPAR) α is a key transcription factor in mediating a magnitude of adaptive responses to fasting. In this study, we examined the role of PPARα in regulation of the hypothalamus-pituitary-thyroid axis. Thyroid-stimulating hormone β-subunit (TSHβ) mRNA abundance was being reduced in response to treatment of TαT1 cells with PPARα agonists (p < 0.05), indicating an inhibitory transcriptional regulation of TSHβ by PPARα. As expected, fasting significantly downregulated TSHβ mRNA expression in a two-factorial study with fed or fasted wild-type (WT) and PPARα knockout mice (p < 0.05). In contrast to the in vitro data, fasted PPARα knockout mice revealed lower mRNA concentrations of pituitary TSHβ (-64%) and TSH-regulated thyroid genes, and lower plasma concentrations of thyroxine (T4, -25%), triiodothyronine (T3, -25%), free T4 (-60%), and free T3 (-35%) than fasted WT mice (p < 0.05). Those differences were not observed in fed mice. Data from thyrotrope cells revealed that PPARα could contribute to the fasting-associated downregulation of the TSHβ mRNA expression. In a mouse model, fasting led to a significant reduction in TSHβ mRNA level, but unexpectedly this effect was stronger in mice lacking PPARα than in WT mice.

Abstract 443: Peroxisome Proliferator Activated Receptor-α Gene Deletion Exacerbates the Progression of Hypertension and Inflammation in Chronic Angiotensin II-Hypertensive Mice

The anti-inflammatory properties of peroxisome proliferator activated receptor- (PPAR-α) contribute to the incidence of hypertension and its associated cardiovascular disease. Fenofibrate, a PPAR-α agonist has been demonstrated to reduce angiotensin II (Ang II)-induced hypertension via inducing cytochrome P450 4A (CYP4A) and increasing 20-hydroxyeicosatetraenoic acid (20-HETE) production. The current study determines whether deletion of PPAR-α gene exacerbates the elevation in blood pressure, plasma interleukin-6 (IL-6) levels, and renal inflammatory markers during infusion of a slow-pressor dose of Ang II (400 ng/kg/min). Ten to twelve week old male PPAR-α knockout (KO) mice and their B129s wild-type (WT) controls were implanted with telemetry devices and infused with Ang II for 12 days. There was no difference in basal mean arterial pressure (MAP) between WT and PPAR-α KO mice compared to WT (113 ± 1 vs. 111 ± 2 mmHg). On day 14 of Ang II infusion, MAP was elevated in PPAR-α KO mice compared to WT (160 ± 3 vs. 142 ± 4 mmHg, P &lt; 0.05) and fenofibrate administration significantly reduced the elevation in MAP in WT + Ang II mice (134 ± 7 mmHg, P &lt; 0.05) with no significant effect on PPAR-α KO + Ang II mice (158 ± 8 mmHg). Plasma IL-6 levels were significantly higher in PPAR-α KO mice when compared to WT on day 12 of Ang II infusion (30 ± 4 vs. 8 ± 2 pg/ml, P &lt; 0.05) and fenofibrate significantly reduced plasma IL-6 in Ang II-treated WT mice (10 ± 3 pg/ml, P &lt; 0.05) with no significant effect in Ang II-treated PPAR-α KO mice (28 ± 4 pg/ml). Fenofibrate significantly increased renal expression of CYP4A and restored the decrease in renal CYP2J expression in WT + Ang II treated mice with no effect on PPAR-α KO + Ang II. Fenofibrate also significantly reduced the elevation in renal expression of the inflammatory markers intracellular adhesion molecule-1 (ICAM-1), monocyte chemoattractant protein-1 (MCP-1) and cyclooxygenase-2 (COX-2) in WT + Ang II mice. Our results demonstrate that PPAR-α KO mice have a greater presser response during Ang II hypertension and activation of PPAR-α attenuates Ang II-induced hypertension possibly via up-regulation of renal CYP4A and CYP2J and anti-inflammatory mechanisms involving reducing the inflammatory markers IL-6, MCP-1, ICAM-1 and COX-2.

Abstract 365: Differential Regulation of NOX2, NOX4 and SOD Expression in the Heart and Kidneys by PPAR-α During Angiotensin II Hypertension

Previous reports suggest peroxisome proliferator-activated receptor-α (PPAR-α) agonist attenuates hypertension by suppressing oxidative stress and increasing superoxide dismutase (SOD) activity. We tested the hypothesis that the absence of PPAR-α would increase NADPH oxidase (NOX)2, NOX4 and decrease SOD expression in mice heart and kidneys during Ang II hypertension. Male (10 - 12 weeks old) PPAR-α knockout (KO) mice and their wild-type (WT) controls were implanted with biotelemetry devices and infused with a slow pressor dose of Ang II (400 ng/kg/min) for 12 days. Separate groups of KO + Ang II and WT + Ang II mice were given the NOX inhibitor, apocynin (1 g/L) or PPAR-α agonist, fenofibrate (145 mg/kg/day). Mean arterial pressure (MAP) was similar between KO (119 ± 2 mmHg) and WT (122 ± 2 mmHg) during the control period. On day 12 of Ang II, MAP was significantly higher in KO than WT, 161 ± 5 and 145 ± 4 mmHg, respectively. Fenofibrate significantly reduced MAP in WT + Ang II mice (134 ± 5 mmHg) and apocynin reduced MAP in KO + Ang II and WT + Ang II mice. Heart and kidney NOX2 expression were significantly increased (61 ± 5% and 33 ± 5 %, respectively) in KO + Ang II when compared to WT + Ang II mice. Apocynin treatment significantly reduced heart and kidney NOX2 expression in KO + Ang II mice. Heart NOX4 expression was significantly decreased (28 ± 3%) in WT + Ang II mice when compared to WT controls. No significant changes were observed in KO + Ang II heart NOX4 expression. Kidney NOX4 expression was significantly decreased in both Ang II-treated KO (77 ± 5%) and WT (50 ± 5%) mice when compared to their respective controls. WT + Ang II SOD expression in the heart was significantly lower than WT controls. Ang II did not lower heart SOD expression in KO mice. SOD expression in the kidneys was significantly decreased in KO + Ang II and WT + Ang II when compared to their respective controls. Fenofibrate significantly increased kidney SOD expression in WT + Ang II mice above WT controls. Fenofibrate did not significantly increase kidney SOD expression in KO + Ang II mice above KO controls. Our results suggest that increased heart and kidney NOX2 expression, along with decreased SOD expression in PPAR-α KO mice contributes to significant increases in MAP during Ang II hypertension.

PPAR‐α regulates NOX2 and SOD expression in the heart during Angiotensin II hypertension

Previous reports suggest peroxisome proliferator‐activated receptor‐α (PPAR‐α) agonist attenuates hypertension by suppressing oxidative stress and increasing superoxide dismutase (SOD) activity. We tested the hypothesis that the absence of PPAR‐α would increase NOX2 and decrease SOD expression in mice hearts during Angiotensin II (ANG II) hypertension. Ten to twelve week old male PPAR‐α knockout (KO) mice and their wild‐type (WT) controls were implanted with biotelemetry devices and infused with ANG II (400 ng/kg/min) for twelve days. Separate groups of PPAR‐α KO and WT mice were treated with ANG II plus apocynin (1 g/1L) and ANG II + fenofibrate (500 mg/kg/day). Mean arterial pressure (MAP) and heart rates (HR) were similar between PPAR‐α KO and WT mice during the control period. On day twelve of ANG II treatment, MAP was significantly higher in PPAR‐α KO than WT, 161 ± 5 and 145 ± 4 mmHG, respectively. Fenofibrate significantly reduced MAP in ANG II treated WT mice (134 ± 5 mmHg) and apocynin reduced MAP in both ANG II treated PPAR‐α KO and WT mice. NOX2 expression was significantly increased in ANG II‐treated PPAR‐α KO mice hearts with no significant changes in ANG II‐treated WT mice. Apocynin significantly reduced NOX2 expression in ANG II‐treated PPAR‐α KO mice with no changes in WT. SOD expression in ANG II + fenofibrate was significantly higher than ANG II‐treated WT mice, with no differences between ANG II + fenofibrate and ANG II‐treated PPAR‐α KO. Our results suggest that increased NOX2 and decreased SOD expression in PPAR‐α KO mice hearts contributes to the significant increases in MAP during ANG II hypertension.

Perfluorooctanoic acid effects on ovaries mediate its inhibition of peripubertal mammary gland development in Balb/c and C57Bl/6 mice

Exposure to perfluorooctanoic acid (PFOA), a synthetic perfluorinated compound and an agonist of peroxisome proliferator-activated receptor α (PPARα), causes stunted mouse mammary gland development in various developmental stages. However, the underlying mechanisms remain poorly understood. We found that peripubertal PFOA exposure significantly inhibited mammary gland growth in both Balb/c and C57Bl/6 wild type mice, but not in C57Bl/6 PPARα knockout mice, and Balb/c mice were more sensitive to PFOA inhibition. PFOA caused (1) delayed or absence of vaginal opening and lack of estrous cycling during the experimental period; (2) decreases in ovarian steroid hormonal synthetic enzyme levels; and (3) reduced expression of estrogen- or progesterone-induced mammary growth factors. Supplementation with exogenous estrogen and/or progesterone reversed the PFOA inhibitory effect on mammary gland. These results indicate that PFOA effects on ovaries mediate its inhibition of mammary gland development in Balb/c and C57Bl/6 mice and that PPARα expression is a contributing factor.

Multiplicity of nuclear receptor activation by PFOA and PFOS in primary human and rodent hepatocytes

Perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS) are surface active fluorochemicals that, due to their exceptional stability to degradation, are persistent in the environment. Both PFOA and PFOS are eliminated slowly in humans, with geometric mean serum elimination half-lives estimated at 3.5 and 4.8 years, respectively. The biological activity of PFOA and PFOS in rodents is attributed primarily to transactivation of the nuclear receptor peroxisome proliferator activated receptor alpha (PPARA), which is an important regulator of lipid and carbohydrate metabolism. However, there are significant species-specific differences in the response to PFOA and PFOS exposure; non-rodent species, including humans, are refractory to several but not all of these effects. Many of the metabolic effects have been attributed to the activation of PPARA; however, recent studies using PPARα knockout mice demonstrate residual PPARA-independent effects, some of which may involve the activation of alternate nuclear receptors, including NR1I2 (PXR), NR1I3 (CAR), NR1H3 (LXRA), and NR1H4 (FXR). The objective of this investigation was to characterize the activation of multiple nuclear receptors and modulation of metabolic pathways associated with exposure to PFOA and PFOS, and to compare and contrast the effects between rat and human primary liver cells using quantitative reverse transcription PCR (RT-qPCR). Our results demonstrate that multiple nuclear receptors participate in the metabolic response to PFOA and PFOS exposure resulting in a substantial shift from carbohydrate metabolism to fatty acid oxidation and hepatic triglyceride accumulation in rat liver cells. This shift in intermediary metabolism was more pronounced for PFOA than PFOS. Furthermore, while there is some similarity in the activation of metabolic pathways between rat and humans, particularly in PPARA regulated responses; the changes in primary human cells were more subtle and possibly reflect an adaptive metabolic response rather than an overt metabolic regulation observed in rodents.

Peroxisome proliferator-activated receptor-α is renoprotective in doxorubicin-induced glomerular injury

Doxorubicin (DOX) is an anthracycline antibiotic utilized in antitumor therapy; however, its clinical use is frequently impeded by renal toxic effects. As peroxisome proliferator-activated receptor-α (PPAR-α) has renoprotective effects in drug-related kidney injuries, we tested its ability to inhibit DOX-induced renal injury. Although both male PPAR-α knockout mice and their wild-type littermates (pure 129/SvJ background) had significant proteinuria 4 weeks after DOX treatment, those with deletion of PPAR-α had more severe proteinuria. This was associated with more serious podocyte foot process effacement compared with wild-type mice. In contrast, the PPAR-α agonist fenofibrate effectively reduced proteinuria and attenuated DOX-induced podocyte foot process effacement. Consistently, glomerular nephrin expression was significantly lower in the knockout compared with wild-type mice following DOX treatment. Fenofibrate therapy significantly blunted the reduction in glomerular nephrin levels in DOX-treated wild-type mice. In cultured podocytes, DOX induced apoptosis, increased cleaved caspase-3 levels, and decreased Bcl-2 expression, all attenuated by pretreatment with fenofibrate. Thus, PPAR-α deficiency exacerbates DOX-related renal injury, in part, due to increased podocyte apoptosis.

PPARα mediates the anti‐inflammatory effect of simvastatin in an experimental model of zymosan‐induced multiple organ failure

Zymosan-induced non-septic shock is a multi-factorial pathology that involves several organs including the kidneys, liver and lungs. Its complexity and diversity presents a continuing therapeutic challenge. Given their pleiotropic effect, statins could be beneficial in non-septic shock. One of the molecular mechanisms underlying the anti-inflammatory effect of statins involves the peroxisome proliferator-activated receptor (PPAR) α. We used a zymosan-induced non-septic shock experimental model to investigate the role of PPARα in the anti-inflammatory effects of simvastatin. Effects of simvastatin (5 or 10 mg·kg(-1) i.p.) were analysed in PPARα knock-out (KO) and PPARα wild type (WT) mice after zymosan or vehicle administration. Organ injury in lung, liver, kidney and intestine was evaluated by immunohistology. PPARα mRNA expression and nuclear factor-κB activation were evaluated in all experimental groups, 18 h after study onset. Cytokine levels were measured in plasma, and nitrite/nitrate in plasma and peritoneal exudate. Nitric oxide synthase, nitrotyrosine and poly ADP-ribose were localized by immunohistochemical methods. Simvastatin significantly and dose-dependently increased the zymosan-induced expression of PPARα levels in all tissues analysed. It also dose-dependently reduced systemic inflammation and the organ injury induced by zymosan in lung, liver, intestine and kidney. These effects were observed in PPARαWT mice and in PPARαKO mice. Simvastatin protected against the molecular and cellular damage caused by systemic inflammation in our experimental model. Our results also provide new information regarding the role of PPARα in the anti-inflammatory effects of statins.

Interactions of PPARα and Acid Sensing Ion Channels on Cerebral Perfusion in Mice

Acid sensing ion channels (ASICs) are expressed in the brain and are made up of various proton sensitive channels which play critical roles in cellular physiology. Different genes have been shown to code for these channels. PPARα, a nuclear transcription factor that regulates many genes is also expressed in the brain and may have a regulatory role in the functions of ASICs. We have investigated the effects of interactions of PPARα and ASICs on the regulation of cerebral perfusion (CP) in mice. Anesthetized wild type (WT) or PPARα knockout (KO) mice received Amiloride (A), ENaC blocker, Benzamil (B), inhibitor of ENaC and Na+/Ca2+ exchange (NCX) blocker; Furosemide (F), inhibitor of Na‐K‐2Cl symporter, or Nigericin (N), ionophore and antiporter of H+ and K+(0.020, 0.35, 6.25, 0.025 mg/kg, respectively). Effects of the treatments were determined by Laser Doppler Scanner (Moor LDI 5152). CP was increased in the WT by 23, 38, or 26% and was attenuated in the KO to −6, 13, or 11% (A, p&lt;0.05), B increased CP in the WT to 24, 38, or 28% and was attenuated to −1, 17, 28% (p&gt;0.05) at 10, 30, or 60 min, respectively (n=3–5, ANOVA). Treatment with F or N reduced CP in the WT and the KO to similar extent. These data indicate that ASICs selectively sensitive to Amiloride and Benzamil are involved in maintaining basal brain perfusion and that PPARα gene is involved. The mechanism for such regulation needs further investigation.

Inhibition of nitric oxide in LPS-stimulated macrophages of young and senescent mice by δ-tocotrienol and quercetin

BackgroundChanges in immune function believed to contribute to a variety of age-related diseases have been associated with increased production of nitric oxide (NO). We have recently reported that proteasome inhibitors (dexamethasone, mevinolin, quercetin, δ-tocotrienol, and riboflavin) can inhibit lipopolysaccharide (LPS)-induced NO production in vitro by RAW 264.7 cells and by thioglycolate-elicited peritoneal macrophages derived from four strains of mice (C57BL/6, BALB/c, LMP7/MECL-1-/- and PPAR-α-/- knockout mice). The present study was carried out in order to further explore the potential effects of diet supplementation with naturally-occurring inhibitors (δ-tocotrienol and quercetin) on LPS-stimulated production of NO, TNF-α, and other pro-inflammatory cytokines involved in the ageing process. Young (4-week-old) and senescent mice (42-week old) were fed control diet with or without quercetin (100 ppm), δ-tocotrienol (100 ppm), or dexamethasone (10 ppm; included as positive control for suppression of inflammation) for 4 weeks. At the end of feeding period, thioglycolate-elicited peritoneal macrophages were collected, stimulated with LPS, LPS plus interferon-β (IFN-β), or LPS plus interferon-γ (IFN-γ), and inflammatory responses assessed as measured by production of NO and TNF-α, mRNA reduction for TNF-α, and iNOS genes, and microarray analysis.ResultsThioglycolate-elicited peritoneal macrophages prepared after four weeks of feeding, and then challenged with LPS (10 ng or 100 ng) resulted in increases of 55% and 73%, respectively in the production of NO of 46-week-old compared to 8-week-old mice fed control diet alone (respective control groups), without affecting the secretion of TNF-α among these two groups. However, macrophages obtained after feeding with quercetin, δ-tocotrienol, and dexamethasone significantly inhibited (30% to 60%; P < 0.02) the LPS-stimulated NO production, compared to respective control groups. There was a 2-fold increase in the production of NO, when LPS-stimulated macrophages of quercetin, δ-tocotrienol, or dexamethasone were also treated with IFN-β or IFN-γ compared to respective control groups. We also demonstrated that NO levels and iNOS mRNA expression levels were significantly higher in LPS-stimulated macrophages from senescent (0.69 vs 0.41; P < 0.05), compared to young mice. In contrast, age did not appear to impact levels of TNF-α protein or mRNA expression levels (0.38 vs 0.35) in LPS-stimulated macrophages. The histological analyses of livers of control groups showed lesions of peliosis and microvesicular steatosis, and treated groups showed Councilman body, and small or large lymphoplasmacytic clusters.ConclusionsThe present results demonstrated that quercetin and δ-tocotrienols inhibit the LPS-induced NO production in vivo. The microarray DNA analyses, followed by pathway analyses indicated that quercetin or δ-tocotrienol inhibit several LPS-induced expression of several ageing and pro-inflammatory genes (IL-1β, IL-1α, IL-6, TNF-α, IL-12, iNOS, VCAM1, ICAM1, COX2, IL-1RA, TRAF1 and CD40). The NF-κB pathway regulates the production of NO and inhibits the pro-inflammatory cytokines involved in normal and ageing process. These ex vivo results confirmed the earlier in vitro findings. The present findings of inhibition of NO production by quercetin and δ-tocotrienol may be of clinical significance treating several inflammatory diseases, including ageing process.

Vaticanol C, a resveratrol tetramer, activates PPARα and PPARβ/δ in vitro and in vivo

BackgroundAppropriate long-term drinking of red wine is associated with a reduced risk of cardiovascular disease. Resveratrol, a well-known SIRT1 activator is considered to be one of the beneficial components contained in red wine, and also developed as a drug candidate. We previously demonstrated that resveratrol protects brain against ischemic stroke in mice through a PPARα-dependent mechanism. Here we report the different effects of the oligomers of resveratrol.MethodsWe evaluated the activation of PPARs by ε-viniferin, a resveratrol dimer, and vaticanol C, a resveratrol tetramer, in cell-based reporter assays using bovine arterial endothelial cells, as well as the activation of SIRT1. Moreover, we tested the metabolic action by administering vaticanol C with the high fat diet to wild-type and PPARα-knockout male mice for eight weeks.ResultsWe show that vaticanol C activates PPARα and PPARβ/δ in cell-based reporter assays, but does not activate SIRT1. ε-Viniferin shows a similar radical scavenging activity as resveratrol, but neither effects on PPARs and SIRT-1. Eight-week intake of vaticanol C with a high fat diet upregulates hepatic expression of PPARα-responsive genes such as cyp4a10, cyp4a14 and FABP1, and skeletal muscle expression of PPARβ/δ-responsive genes, such as UCP3 and PDK4 (pyruvate dehydrogenase kinase, isoform 4), in wild-type, but not PPARα-knockout mice.ConclusionVaticanol C, a resveratrol tetramer, activated PPARα and PPARβ/δ in vitro and in vivo. These findings indicate that activation of PPARα and PPARβ/δ by vaticanol C may be a novel mechanism, affording beneficial effects against lifestyle-related diseases.

Thyroid Hormone Regulates Hepatic Expression of Fibroblast Growth Factor 21 in a PPARα-dependent Manner

Thyroid hormone has profound and diverse effects on liver metabolism. Here we show that tri-iodothyronine (T3) treatment in mice acutely and specifically induces hepatic expression of the metabolic regulator fibroblast growth factor 21 (FGF21). Mice treated with T3 showed a dose-dependent increase in hepatic FGF21 expression with significant induction at doses as low as 100 microg/kg. Time course studies determined that induction is seen as early as 4 h after treatment with a further increase in expression at 6 h after injection. As FGF21 expression is downstream of the nuclear receptor peroxisome proliferator-activated receptor alpha (PPARalpha), we treated PPARalpha knock-out mice with T3 and found no increase in expression, indicating that hepatic regulation of FGF21 by T3 in liver is via a PPARalpha-dependent mechanism. In contrast, in white adipose tissue, FGF21 expression was suppressed by T3 treatment, with other T3 targets unaffected. In cell culture studies with an FGF21 reporter construct, we determined that three transcription factors are required for induction of FGF21 expression: thyroid hormone receptor beta (TRbeta), retinoid X receptor (RXR), and PPARalpha. These findings indicate a novel regulatory pathway whereby T3 positively regulates hepatic FGF21 expression, presenting a novel therapeutic target for diseases such as non-alcoholic fatty liver disease.

Prostacyclin-induced peroxisome proliferator-activated receptor-α translocation attenuates NF-κB and TNF-α activation after renal ischemia-reperfusion injury

Prostacyclin and peroxisome proliferator-activated receptors (PPAR) protect against ischemia-reperfusion (I/R) injury by the induction of an anti-inflammatory pathway. In this study, we examined the prostacyclin-enhanced protective effect of PPARalpha in I/R-induced kidney injury. PPAR-alpha reduced the NF-kappaB-induced overexpression of TNF-alpha and apoptosis in cultured kidney cells. In a murine model, pretreating wild-type (WT) mice with a PPAR-alpha activator, docosahexaenoic acid (DHA), significantly reduced I/R-induced renal dysfunction (lowered serum creatinine and urea nitrogen levels), apoptotic responses (decreased apoptotic cell number and caspase-3, -8 activation), and NF-kappaB activation. By comparison, I/R-induced injury was exacerbated in PPAR-alpha knockout mice. This indicated that PPAR-alpha attenuated renal I/R injury via NF-kappaB-induced TNF-alpha overexpression. Overexpression of prostacyclin using an adenovirus could also induce PPAR-alpha translocation from the cytosol into the nucleus to inhibit caspase-3 activation. This prostacyclin/PPAR-alpha pathway attenuated TNF-alpha promoter activity by binding to NF-kappaB. Using a cAMP inhibitor (CAY10441) and a prostacyclin receptor antibody, we also found that there was another prostacyclin/IP receptor/cAMP pathway that could inhibit TNF-alpha production. Taken together, our results demonstrate for the first time that prostacyclin induces the translocation of PPAR-alpha from the cytosol into the nucleus and attenuates NF-kappaB-induced TNF-alpha activation following renal I/R injury. Treatments that can augment prostacyclin, PPAR-alpha, or the associated signaling pathways may ameliorate conditions associated with renal I/R injury.

Modulation of nutrient sensing nuclear hormone receptors promotes weight loss through appetite suppression in mice

Peroxisome proliferator activated receptors (PPARs) are nuclear receptors involved in glucose and lipid metabolism. Three isoforms of PPARs have been identified with different tissue distribution and biological functions. Although the pharmacology of each receptor is well studied, the physiological effect of simultaneous activation of PPARalpha, gamma and delta is only starting to emerge. We sought to determine the biological effects of a novel PPAR pan activator and elucidate the physiological mechanisms involved. Ob/ob, diet-induced obese (DIO) or PPARalpha knockout mice were administered a novel agonist that activates all PPARs to various degrees to determine the effect on body weight, body composition, food intake and energy expenditure. In addition, serum parameters including glucose, insulin, triglycerides and ketone bodies as well as tissue acylcarnitine were evaluated. The effect of the novel agonist on liver and skeletal muscle histopathology was also studied. We report that simultaneous activation of all PPARs resulted in substantial weight loss in ob/ob and DIO mice. Consistent with known PPAR pharmacology, we observed that agonist treatment increased lipid oxidation, although appetite suppression was mainly responsible for the weight loss. Agonist-induced weight loss was completely absent in PPARalpha knockout mice suggesting that PPARalpha pharmacology was the major contributor to weight regulation in mice. Our work provides evidence that simultaneous activation of PPARalpha, gamma and delta decreases body weight by regulating appetite. These effects of the pan agonist were completely absent in PPARalpha knockout mice, suggesting that PPARalpha pharmacology was the major contributor to weight loss.

Downregulation of peroxisome proliferator-activated receptor α and its coactivators in liver and skeletal muscle mediates the metabolic adaptations during lactation in mice

Previous studies have shown that genes involved in fatty acid uptake, fatty acid oxidation, and thermogenesis are downregulated in liver and skeletal muscle of rats during lactation. However, biochemical mechanisms underlying these important metabolic adaptations during lactation have not yet been elucidated. As all these genes are transcriptionally regulated by peroxisome proliferator-activated receptor alpha (Pparalpha), we hypothesized that their downregulation is mediated by a suppression of Pparalpha during lactation. In order to investigate this hypothesis, we performed an experiment with lactating and nonlactating Pparalpha knockout and corresponding wild-type mice. In wild-type mice, lactation led to a considerable downregulation of Pparalpha, Ppar coactivators Pgc1alpha and Pgc1beta, and Pparalpha target genes involved in fatty acid uptake, fatty acid oxidation, and thermogenesis in liver and skeletal muscle (P<0.05). Pparalpha knockout mice had generally a lower expression of all these Pparalpha target genes in liver and skeletal muscle. However, in those mice, lactation did not lower the expression of genes involved in fatty acid utilization and thermogenesis in liver and skeletal muscle. Expression levels of Pparalpha target genes in lactating wild-type mice were similar than in lactating or nonlactating Pparalpha knockout mice. In conclusion, the present findings suggest that downregulation of Pparalpha and its coactivators in tissues with high rates of fatty acid catabolism is responsible for the reduced utilization of fatty acids in liver and skeletal muscle and the reduced thermogenesis occurring in the lactating animal, which aim to conserve energy and metabolic substrates for milk production in the mammary gland.

Mouse carnitine–acylcarnitine translocase ( CACT) is transcriptionally regulated by PPARα and PPARδ in liver cells

Background Hepatic PPARα acts as the primary mediator of the adaptive response to fasting by upregulation of a number of genes involved in fatty acid catabolism. Whether carnitine–acylcarnitine translocase ( CACT), which mediates the import of acylcarnitines into the mitochondrial matrix for subsequent β-oxidation of fatty acid moieties, is also regulated by PPARα in the liver has not yet been investigated. Methods and Results Herein, we observed that hepatic mRNA abundance of CACT was increased by both, fasting and treatment with PPARα agonist WY-14,643 in wild-type mice but not PPARα-knockout mice ( P < 0.05). Cell culture experiments revealed that CACT mRNA abundance was higher in liver cells treated with either WY-14,643 or PPARδ agonist GW0742, but not with PPARγ agonist troglitazone (TGZ) than in control cells ( P < 0.05). In addition, reporter assays revealed activation of mouse CACT promoter by WY-14,643 and GW0742, but not TGZ. Moreover, deletion and mutation analyses of CACT promoter and 5′-UTR revealed one functional PPRE in the 5′-UTR of mouse CACT. General significance CACT is upregulated by PPARα and PPARδ, probably by binding to a functional PPRE at position + 45 to + 57 relative to the transcription start site. The upregulation of CACT by PPARα and PPARδ, which are both important for the regulation of fatty acid oxidation in tissues during fasting, may increase the import of acylcarnitine into the mitochondrial matrix during fasting.

WHAT IS NEW IN SHOCK, JULY 2009?

WHAT IS NEW IN SHOCK, JULY 2009?

Role of peroxisome proliferator-activated receptor-α in ileum tight junction alteration in mouse model of restraint stress

Restraint stress induces permeability changes in the small intestine, but little is known about the role of endogenous peroxisome proliferator-activated receptor-alpha (PPAR-alpha) ligand in the defects of the tight junction function. In the present study, we used PPAR-alpha knockout mice to understand the roles of endogenous PPAR-alpha on ileum altered permeability function in models of immobilization stress. The absence of a functional PPAR-alpha gene in PPAR-alpha knockout mice resulted in a significant augmentation of the degree of 1) TNF-alpha production in ileum tissues; 2) the alteration of zonula occludens-1, occludin, and beta-catenin (immunohistochemistry); and 3) apoptosis (terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling staining, Bax, Bcl-2 expression). Taken together, our results demonstrate that endogenous PPAR-alpha ligands reduce the degree of tight junction permeability in the ileum tissues associated with immobilization stress, suggesting a possible role of endogenous PPAR-alpha ligands on ileum barrier dysfunction.

PPARα blocks glucocorticoid receptor α-mediated transactivation but cooperates with the activated glucocorticoid receptor α for transrepression on NF-κB

Glucocorticoid receptor alpha (GRalpha) and peroxisome proliferator-activated receptor alpha (PPARalpha) are transcription factors with clinically important immune-modulating properties. Either receptor can inhibit cytokine gene expression, mainly through interference with nuclear factor kappaB (NF-kappaB)-driven gene expression. The present work aimed to investigate a functional cross-talk between PPARalpha- and GRalpha-mediated signaling pathways. Simultaneous activation of PPARalpha and GRalpha dose-dependently enhances transrepression of NF-kappaB-driven gene expression and additively represses cytokine production. In sharp contrast and quite unexpectedly, PPARalpha agonists inhibit the expression of classical glucocorticoid response element (GRE)-driven genes in a PPARalpha-dependent manner, as demonstrated by experiments using PPARalpha wild-type and knockout mice. The underlying mechanism for this transcriptional antagonism relies on a PPARalpha-mediated interference with the recruitment of GRalpha, and concomitantly of RNA polymerase II, to GRE-driven gene promoters. Finally, the biological relevance of this phenomenon is underscored by the observation that treatment with the PPARalpha agonist fenofibrate prevents glucocorticoid-induced hyperinsulinemia of mice fed a high-fat diet. Taken together, PPARalpha negatively interferes with GRE-mediated GRalpha activity while potentiating its antiinflammatory effects, thus providing a rationale for combination therapy in chronic inflammatory disorders.

Review of the expression of peroxisome proliferator-activated receptors alpha (PPARα), beta (PPARβ), and gamma (PPARγ) in rodent and human development

The peroxisome proliferator-activated receptors (PPAR) belong to the nuclear hormone receptor superfamily and there are three primary subtypes, PPARα, β, and γ. These receptors regulate important physiological processes that impact lipid homeostasis, inflammation, adipogenesis, reproduction, wound healing, and carcinogenesis. These nuclear receptors have important roles in reproduction and development and their expression may influence the responses of an embryo exposed to PPAR agonists. PPARs are relevant to the study of the biological effects of the perfluorinated alkyl acids as these compounds, including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), activate PPARα. Exposure of the rodent to PFOA or PFOS during gestation results in neonatal deaths, developmental delay and growth deficits. Studies in PPARα knockout mice demonstrate that the developmental effects of PFOA, but not PFOS, depend on expression of PPARα. This review provides an overview of PPARα, β, and γ protein and mRNA expression during mouse, rat, and human development. The review presents the results from many published studies and the information is organized by organ system and collated to show patterns of expression at comparable developmental stages for human, mouse, and rat. The features of the PPAR nuclear receptor family are introduced and what is known or inferred about their roles in development is discussed relative to insights from genetically modified mice and studies in the adult.