PPARβ Agonist Research Articles

Pectolinarigenin ameliorates osteoporosis via enhancing Wnt signaling cascade in PPARβ-dependent manner

BackgroundOsteoporosis is a prevalent metabolic bone disease in older adults. Peroxisome proliferator-activated receptor β (PPARβ), the most abundant PPAR isotype expressed in bone tissues, plays a critical role in regulating the energy metabolism of osteoblasts. However, the botanical compounds targeting PPARβ for the treatment of osteoporosis remain largely unexplored. PurposeTo discover a potent PPARβ agonist from botanical compounds, as well as to investigate the anti-osteoporosis effects and to elucidate the underlying mechanisms of the newly identified PPARβ agonist. MethodsThe PPARβ agonist effects of botanical compounds were screened by an in vitro luciferase reporter gene assay. The PPARβ agonist effects of pectolinarigenin (PEC) in bone marrow mesenchymal stromal cells (BMSCs) were validated by Western blotting. RNA-seq transcriptome analyses were conducted to reveal the underlying osteoporosis mechanisms of PEC in BMSCs. The PPARβ antagonist (GSK0660) and Wnt signaling inhibitor (XAV969) were used to explore the role of the PPARβ and Wnt signaling cascade in the anti-osteoporosis effects of PEC. PEC or the PEG-PLGA nanoparticles of PEC (PEC–NP) were intraperitoneally administrated in both wild-type mice and ovariectomy-induced osteoporosis mice to examine its anti-osteoporotic effects in vivo. ResultsPEC, a newly identified naturally occurring PPARβ agonist, significantly promotes osteogenic differentiation and up-regulates the osteogenic differentiation-related genes (Runx2, Osterix, and Bmp2) in BMSCs. RNA sequencing and functional gene enrichment analysis suggested that PEC could activate osteogenic-related signaling pathways, including Wnt and PPAR signaling pathways. Further investigations suggested that PEC could enhance Wnt/β-catenin signaling in a PPARβ-dependent manner in BMSCs. Animal tests showed that PEC–NP promoted bone mass and density, increased the bone cell matrix protein, and accelerated bone formation in wild-type mice, while PEC–NP also played a preventive role in ovariectomy-induced osteoporosis mice via maintaining the expression level of bone cell matrix protein, balancing the rate of bone formation, and slowing down bone loss. Additionally, PEC–NP did not cause any organ injury and body weight loss after long-term use (11 weeks). ConclusionPEC significantly promotes bone formation and reduces bone loss in both BMSCs and ovariectomy-induced osteoporosis mice via enhancing the Wnt signaling cascade in a PPARβ-dependent manner, providing a new alternative therapy for preventing estrogen deficiency-induced osteoporotic diseases.

Muscle-building supplement β-hydroxy β-methylbutyrate stimulates the maturation of oligodendroglial progenitor cells to oligodendrocytes.

Oligodendrocytes are the myelinating cells in the CNS and multiple sclerosis (MS) is a demyelinating disorder that is characterized by progressive loss of myelin. Although oligodendroglial progenitor cells (OPCs) should be differentiated into oligodendrocytes, for multiple reasons, OPCs fail to differentiate into oligodendrocytes in MS. Therefore, increasing the maturation of OPCs to oligodendrocytes may be of therapeutic benefit for MS. The β-hydroxy β-methylbutyrate (HMB) is a muscle-building supplement in humans and this study underlines the importance of HMB in stimulating the maturation of OPCs to oligodendrocytes. HMB treatment upregulated the expression of different maturation markers including PLP, MBP, and MOG in cultured OPCs. Double-label immunofluorescence followed by immunoblot analyses confirmed the upregulation of OPC maturation by HMB. While investigating mechanisms, we found that HMB increased the maturation of OPCs isolated from peroxisome proliferator-activated receptor β-/- (PPARβ-/-) mice, but not PPARα-/- mice. Similarly, GW6471 (an antagonist of PPARα), but not GSK0660 (an antagonist of PPARβ), inhibited HMB-induced maturation of OPCs. GW9662, a specific inhibitor of PPARγ, also could not inhibit HMB-mediated stimulation of OPC maturation. Furthermore, PPARα agonist GW7647, but neither PPARβ agonist GW0742 nor PPARγ agonist GW1929, alone increased the maturation of OPCs. Finally, HMB treatment of OPCs led to the recruitment of PPARα, but neither PPARβ nor PPARγ, to the PLP gene promoter. These results suggest that HMB stimulates the maturation of OPCs via PPARα and that HMB may have therapeutic prospects in remyelination.

371 Activated PPARβ/QKI Signaling in Macrophage/Microglia Sensitizes Glioblastoma to Immunotherapy

INTRODUCTION: Glioblastomas (GBMs) share overwhelmingly immunosuppressive tumor microenvironments that are enriched in glioblastoma-associated macrophages and microglia (GAMs). Notably, GAMs have distinctive reshuffling of lipid composition and dysfunctional lipid metabolism. The peroxisome proliferator-activated receptor (PPAR) family members are master regulators of lipid metabolism in macrophages. One of the PPARs, PPARβ is a pivotal modulator of lipid metabolism in macrophages that orchestrates timely disposal of GBM cells. METHODS: Co-immunoprecipitation using an anti-Qki antibody was followed by detecting PPARβ. PPARβ and QKI levels were compared between GAMs inside GBMs and paired macrophages/microglia outside GBMs, as well as human low-grade versus high-grade gliomas. Survival was collected from CX3CR1-CreERT2; PpardL/L/Qki+/+ mice (PPARβ KO) (Ppard is the gene name for PPARβ), CX3CR1-CreERT2; Ppard+/+/QkiL/L mice (QKI KO) and control CX3CR1-CreERT2; Ppard+/+/Qki+/+ (Ctrl) mice given tamoxifen when implanted with GL261 cells. Survival was collected for GBM bearing mice given PPARβ agonist, KD3010 and/or anti-PD-1 therapy. RESULTS: PPARβ co-activates the QKI-mediated complex, which is an essential mediator of phagocytosis in macrophage/microglia. Moreover, PPARβ/QKI signaling is markedly decreased in GAMs relative to paired macrophages/microglia within boundary brain parenchyma (P < 0.001). Myeloid cell–specific PPARβ; or QKI knockout shorten overall survival of GBM–bearing mice (P < 0.05), and inhibited PPARβ/QKI signaling in GAMs correlates with grade progression in human gliomas (P < 0.01) and worse prognosis for GBM (P = 0.0034). Therapeutically, PPARβ agonist plus anti-PD-1 greatly prolongs survival of mice GBMs relative to anti-PD-1 monotherapy (P < 0.05). CONCLUSIONS: We characterize dysfunctional lipid metabolism in GAMs and elucidates the mechanism underlying immunosuppression of GAMs caused by PPARβ/QKI loss. The study supports for therapeutic options for restoring PPARβ/QKI-mediated lipid metabolism in GAMs and development of novel strategies to sensitize GBM to immunotherapy.

PPARβ down-regulation is involved in high glucose-induced endothelial injury via acceleration of nitrative stress.

Endothelial injury plays a vital role in vascular lesions from diabetes mellitus (DM). Therapeutic targets against endothelial damage may provide critical venues for the treatment of diabetic vascular diseases. Peroxisome proliferator-activated receptor β (PPARβ) is a crucial regulator in DM and its complications. However, the molecular signal mediating the roles of PPARβ in DM-induced endothelial dysfunction is not fully understood. The impaired endothelium-dependent relaxation and destruction of the endothelium structures appeared in high glucose incubated rat aortic rings. A high glucose level significantly decreased the expression of PPARβ and endothelial nitric oxide synthase (eNOS) at the mRNA and protein levels, and reduced the concentration of nitric oxide (NO), which occurred in parallel with an increase in the expression of inducible nitric oxide synthase (iNOS) and 3-nitrotyrosine. The effect of high glucose was inhibited by GW0742, a PPARβ agonist. Both GSK0660 (PPARβ antagonist) and NG-nitro-l-arginine-methyl ester (NOS inhibitor) could reverse the protective effects of GW0742. These results suggest that the activation of nitrative stress may, at least in part, mediate the down-regulation of PPARβ in high glucose-impaired endothelial function in rat aorta. PPARβ-nitrative stress may hold potential in treating vascular complications from DM.

Comparison of PPAR Ligands as Modulators of Resolution of Inflammation, via Their Influence on Cytokines and Oxylipins Release in Astrocytes

Neuroinflammation is a key process of many neurodegenerative diseases and other brain disturbances, and astrocytes play an essential role in neuroinflammation. Therefore, the regulation of astrocyte responses for inflammatory stimuli, using small molecules, is a potential therapeutic strategy. We investigated the potency of peroxisome proliferator-activated receptor (PPAR) ligands to modulate the stimulating effect of lipopolysaccharide (LPS) in the primary rat astrocytes on (1) polyunsaturated fatty acid (PUFAs) derivative (oxylipins) synthesis; (2) cytokines TNFα and interleukin-10 (IL-10) release; (3) p38, JNK, ERK mitogen-activated protein kinase (MAPKs) phosphorylation. Astrocytes were exposed to LPS alone or in combination with the PPAR ligands: PPARα (fenofibrate, GW6471); PPARβ (GW501516, GSK0660); PPARγ (rosiglitazone, GW9662). We detected 28 oxylipins with mass spectrometry (UPLC-MS/MS), classified according to their metabolic pathways: cyclooxygenase (COX), cytochrome P450 monooxygenases (CYP), lipoxygenase (LOX) and PUFAs: arachidonic (AA), docosahexaenoic (DHA), eicosapentaenoic (EPA). All tested PPAR ligands decrease COX-derived oxylipins; both PPARβ ligands possessed the strongest effect. The PPARβ agonist, GW501516 is a strong inducer of pro-resolution substances, derivatives of DHA: 4-HDoHE, 11-HDoHE, 17-HDoHE. All tested PPAR ligands decreased the release of the proinflammatory cytokine, TNFα. The PPARβ agonist GW501516 and the PPARγ agonist, rosiglitazone induced the IL-10 release of the anti-inflammatory cytokine, IL-10; the cytokine index, (IL-10/TNFα) was more for GW501516. The PPARβ ligands, GW501516 and GSK0660, are also the strongest inhibitors of LPS-induced phosphorylation of p38, JNK, ERK MAPKs. Overall, our data revealed that the PPARβ ligands are a potential pro-resolution and anti-inflammatory drug for targeting glia-mediated neuroinflammation.

Peroxisome Proliferator Activated Receptor Beta (PPARβ) activity increases the immune response and shortens the early phases of skeletal muscle regeneration

Peroxisome Proliferator-Activated Receptor Beta (PPARβ) is a transcription factor playing an important role in both muscle myogenesis and remodeling, and in inflammation. However, its role in the coordination of the transient muscle inflammation and reparation process following muscle injury has not yet been fully determined. We postulated that activation of the PPARβ pathway alters the early phase of the muscle regeneration process, i.e. when immune cells infiltrate in injured muscle. Tibialis anteriors of C57BL6/J mice treated or not with the PPARβ agonist GW0742 were injected with cardiotoxin (or with physiological serum for the contralateral muscle). Muscle regeneration was monitored on days 4, 7, and 14 post-injury. We found that treatment of mice with GW0742 increased, at day 4 post-damage, the recruitment of immune cells (M1 and M2 macrophages) and upregulated the expression of the anti-inflammatory cytokine IL-10 and TGF-β mRNA. Those effects were accompanied by a significant increase at day 4 of myogenic regulatory factors (Pax7, MyoD, Myf5, Myogenin) mRNA in GW0742-treated mice. However, we showed an earlier return (7 days vs 14 days) of Myf5 and Myogenin to basal levels in GW0742- compared to DMSO-treated mice. Differential effects of GW0742 observed during the regeneration were associated with variations of PPARβ pathway activity. Collectively, our findings indicate that PPARβ pathway activity shortens the early phases of skeletal muscle regeneration by increasing the immune response.

PPAR ligand association with prostaglandin F2α and E2 synthesis in the pig corpus luteum—An in vitro study

The present study evaluated the involvement of PPARs in prostaglandin (PG) E2 and F2α production in the corpus luteum (CL) of pigs on days 10–12 and 14–16 of the estrous cycle or pregnancy. The tissue explants were incubated for 6h in the presence of PPARα, PPARβ, PPARγ ligands. The concentration of PGs in the incubation media was determined by radioimmunoassay, while mRNA abundance of PG synthetases (PGES and PGFS) was analyzed by quantitative real-time PCR. It was found that L-165,045 and rosiglitazone stimulated PGES synthesis on days 10–12 of the estrous cycle, whereas all factors that were assessed did not affect PGE2 release. The PGFS mRNA abundance in the CL did not change in the presence of PPAR ligands during the assessment periods. However, PPARβ agonist inhibited PGF2α secretion on days 10–12 of the estrous cycle and on days 14–16 of pregnancy. Interestingly, PPAR antagonists, MK 886, GW 9662 or T0070907 decreased PGF2α release by the slices on days 10–12 of the estrous cycle. It is concluded that the CL has a different susceptibility (greatest during mid-luteal phase of the estrous cycle) to the PPAR ligands, which is related to the physiological status of animal. The inhibition of PGF2α release and augmentation of PGES mRNA concentration during mid-luteal phase of the estrous cycle might suggest luteotropic properties of PPAR ligands.

A Flavonoid Compound Promotes Neuronal Differentiation of Embryonic Stem Cells via PPAR-β Modulating Mitochondrial Energy Metabolism.

Relatively little is known regarding mitochondrial metabolism in neuronal differentiation of embryonic stem (ES) cells. By using a small molecule, present research has investigated the pattern of cellular energy metabolism in neural progenitor cells derived from mouse ES cells. Flavonoid compound 4a faithfully facilitated ES cells to differentiate into neurons morphologically and functionally. The expression and localization of peroxisome proliferator-activated receptors (PPARs) were examined in neural progenitor cells. PPAR-β expression showed robust upregulation compared to solvent control. Treatment with PPAR-β agonist L165041 alone or together with compound 4a significantly promoted neuronal differentiation, while antagonist GSK0660 blocked the neurogenesis-promoting effect of compound 4a. Consistently, knockdown of PPAR-β in ES cells abolished compound 4a-induced neuronal differentiation. Interestingly, we found that mitochondrial fusion protein Mfn2 was also abolished by sh-PPAR-β, resulting in abnormal mitochondrial Ca2+ ([Ca2+]M) transients as well as impaired mitochondrial bioenergetics. In conclusion, we demonstrated that by modulating mitochondrial energy metabolism through Mfn2 and mitochondrial Ca2+, PPAR-β took an important role in neuronal differentiation induced by flavonoid compound 4a.

Vascular and Central Activation of Peroxisome Proliferator-Activated Receptor-β Attenuates Angiotensin II-Induced Hypertension: Role of RGS-5.

Activation of peroxisome proliferator-activated receptor-β/δ (PPARβ) lowers blood pressure in genetic and mineralocorticoid-induced hypertension. Regulator of G-protein-coupled receptor signaling 5 (RGS5) protein, which interferes in angiotensin II (AngII) signaling, is a target gene to PPARβ The aim of the present study was to examine whether PPARβ activation in resistance arteries and brain tissues prevents the elevated blood pressure in AngII-induced hypertension and evaluate the role of RGS5 in this effect. C57BL/6J male mice were divided into five groups (control mice, PPARβ agonist [4-[[[2-[3-Fluoro-4-(trifluoromethyl)phenyl]-4-methyl-5-thiazolyl]methyl]thio]-2-methylphenoxy]acetic acid (GW0742)-treated mice AngII-infused mice, GW0742-treated AngII-infused mice, and AngII-infused mice treated with GW0742 plus PPARβ antagonist 3-[[[2-Methoxy-4-(phenylamino)phenyl]amino]sulfonyl]-2-thiophenecarboxylic acid methyl ester (GSK0660)) and were followed for 3 weeks. GW0742 prevented the increase in both arterial blood pressure and plasma noradrenaline levels and the higher reduction of blood pressure after ganglionic blockade, whereas it reduced the mesenteric arterial remodeling and the hyper-responsiveness to vasoconstrictors (AngII and endothelin-1) in AngII-infused mice. These effects were accompanied by an inhibition of NADPH oxidase expression and activity in the brain. Gene expression profiling revealed a marked loss of brainstem and vascular RGS5 in AngII-infused mice, which was restored by GW0742. GW0742-induced effects were abolished by GSK0660. Small interfering RNA targeting RGS5 caused augmented contractile response to AngII in resistance mesenteric arteries and blunted the inhibitory effect of GW0742 on this response. In conclusion, GW0742 exerted antihypertensive effects, restoring sympathetic tone and vascular structure and function in AngII-infused mice by PPARβ activation in brain and vessels inhibiting AngII signaling as a result of RGS5 upregulation.

α-Lipoic acid up-regulates expression of peroxisome proliferator-activated receptor β in skeletal muscle: involvement of the JNK signaling pathway.

We hypothesized that α-lipoic acid (α-LA) might interact with the transcriptional control of peroxisome proliferator-activated receptor (PPAR)β in skeletal muscle. Molecular mechanisms were investigated using differentiated C2C12 myotubes treated with α-LA and/or PPARβ agonist GW0742. In vivo studies with 3-mo-old C57Bl6 mice were realized: voluntary wheel running (VWR) training (7 wk), and a 6 wk diet containing (or not) α-LA (0.25% wt/wt). This last condition was combined with (or not) 1 bout of treadmill exercise (18 m/min for 1 h). Using a reporter assay, we demonstrate that α-LA is not an agonist of PPARβ but regulates PPARβ target gene expression through an active PPARβ pathway. GW0742-induced pyruvate dehydrogenase kinase 4 mRNA is potentiated by α-LA. In C2C12, α-LA lowers the activation of the JNK signaling pathway and increases PPARβ mRNA and protein levels (2-fold) to the same extent as with the JNK inhibitor SP600125. Similarly to VWR training effect, PPARβ expression increases (2-fold) in vastus lateralis of animals fed an α-LA-enriched diet. However, α-LA treatment does not further stimulate the adaptive up-regulation of PPARβ observed in response to 1 bout of exercise. We have identified a novel mechanism of regulation of PPARβ expression/action in skeletal muscle with potential physiologic application through the action of α-LA, involving the JNK pathway.

Regulation of cyclooxygenase 2 expression by agonists of PPAR nuclear receptors in the model of endotoxin tolerance in astrocytes.

Endotoxin tolerance (ET) represents a state of an altered immune response induced by multiple stimulations of a cell, a tissue, or an organism with lipopolysaccharide. Characteristics of ET include downregulation of induction of proinflammatory genes (TNFα, IL6, and others) and enhancement of induction of antiinflammatory genes (IL10, TGFβ). ET generally has protective functions; nevertheless, it might result in a state of innate immune deficiency and cause negative outcomes. A current issue is the search for the mechanisms controlling the level of inflammation in the course of endotoxin tolerance. In this work, we investigated the change in cyclooxygenase 2 (Cox2) expression in the model of endotoxin tolerance in astrocytes and analyzed the possibility of regulating this process applying nuclear receptor PPAR agonists. Our results indicate that: 1) endotoxin tolerance can be induced in astrocytes and results in TNFα and Cox2 mRNA induction decrease upon secondary stimulation; 2) tolerance is revealed on the level of TNFα release and Cox2 protein expression; 3) PPAR agonists GW7647, L-165041, and rosiglitazone control Cox2 mRNA expression levels under conditions of endotoxin tolerance. In particular, rosiglitazone (a PPARγ agonist) induces Cox2 mRNA expression, while GW7647 (a PPARα agonist) and L-165041 (a PPARβ agonist) suppress the expression. Our results demonstrate that Cox2 can be up- and downregulated during endotoxin tolerance in astrocytes, and PPAR agonists might be effective for controlling this target under conditions of multiple proinflammatory stimulations of brain tissues with endotoxin.

PROTECTIVE EFFECTS OF PEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR (PPAR)-ß ACTIVATION ON LIPID-INDUCED ENDOTHELIAL DYSFUNCTION via CARNITINE PALMITOYL TRANSFERASE-1 UPREGULATION

Peroxisome proliferator-activated receptors (PPARs) have been identified as key endothelial signaling molecules regulating lipid metabolism, and contributing to the metabolic derangements associated with Type 2 Diabetes. We investigated whether PPARβ...

Fatty acid elongase-5 (Elovl5) regulates hepatic triglyceride catabolism in obese C57BL/6J mice

Nonalcoholic fatty liver disease is a major public health concern in the obese and type 2 diabetic populations. The high-fat lard diet induces obesity and fatty liver in C57BL/6J mice and suppresses expression of the PPAR-target gene, FA elongase 5 (Elovl5). Elovl5 plays a key role in MUFA and PUFA synthesis. Increasing hepatic Elovl5 activity in obese mice lowered hepatic TGs and endoplasmic reticulum stress markers (X-box binding protein 1 and cAMP-dependent transcription factor 6α) and increased TG catabolism and fatty acyl carnitines. Increased hepatic Elovl5 activity did not increase hepatic capacity for β-oxidation. Elovl5 effects on hepatic TG catabolism were linked to increased protein levels of adipocyte TG lipase (ATGL) and comparative gene identification 58 (CGI58). Elevated hepatic Elovl5 activity also induced the expression of some (pyruvate dehydrogenase kinase 4 and fibroblast growth factor 21), but not other cytochrome P450 4A10 (CYP4A10), PPAR-target genes. FA products of Elovl5 activity increased ATGL, but not CGI58, mRNA through PPARβ-dependent mechanisms in human HepG2 cells. Treatment of mouse AML12 hepatocytes with the PPARβ agonist (GW0742) decreased (14)C-18:2,n-6 in TGs but did not affect β-oxidation. These studies establish that Elovl5 activity regulates hepatic levels of FAs controlling PPARβ activity, ATGL expression, and TG catabolism, but not FA oxidation.

The PPARβ agonist L-165041 promotes VEGF mRNA stabilization in HPV18-harboring HeLa cells through a receptor-independent mechanism

Peroxisome Proliferator-Activated Receptor-β (PPARβ) is a ligand-inducible transcription factor activated by both natural (fatty acids and derivatives) and high affinity synthetic agonists. It is thought to play a role in angiogenesis development and Vascular Endothelial Growth Factor (VEGF) regulation but its contribution remains unclear. Until now, the PPARβ agonism effect on VEGF expression in cervical cancer cells was unknown. This led to our interest in assessing the effect of PPARβ activation on the regulation of different VEGF isoforms mRNA expression and the impact of E6 viral oncoprotein and its target p53 on this regulation in cervical cancer cells. Here, we showed that the PPARβ agonist L-165041 induces VEGF121, VEGF165 and VEGF189 expression in HPV (Human Papillomavirus) positive HeLa cells but not in HPV negative cells. The underlying mechanisms did involve neither E6 oncoprotein nor p53. We highlighted a novel mode of PPARβ ligand action including a post-transcriptional regulation of VEGF mRNA expression through the p38 MAPK signaling pathway and the activation of the mRNA-stabilizing factor HuR. But most importantly, we clearly demonstrated that L-165041 acts independently of PPARβ since its effect was not reversed by a chemical inhibition with a specific antagonist and the siRNA-mediated knockdown of the nuclear receptor. As VEGF is crucial for cancer development, the impact of PPARβ ligands on VEGF production is of high importance. Thus, the molecular mechanism of their action has to be elucidated and as a result, PPARβ agonists currently in clinical trials should be carefully monitored.

The involvement of peroxisome proliferator activated receptors (PPARs) in prostaglandin F2α production by porcine endometrium

In the present study, we investigated the in vitro effects of peroxisome proliferator activated receptor (PPAR) ligands on PGF2α secretion and mRNA expression of prostaglandin F synthase (PGFS) in porcine endometrial explants collected on days 10–12 and 14–16 of the estrous cycle or pregnancy. The explants were incubated for 6h with: PPARα ligands – WY-14643 (agonist) and MK 886 (antagonist); PPARβ ligands – l-165,041 (agonist) and GW 9662 (antagonist); PPARγ ligands – 15d-prostaglandin J2 (PGJ2, agonist), rosiglitazone (agonist) and T0070907 (antagonist). The expression of PGFS mRNA in the endometrium and the concentration of PGF2α in culture media were determined by real time RT-PCR and radioimmunoassay, respectively. During the estrous cycle (days 10–12 and 14–16), the agonists – WY-14643 (PPARα), l-165,041 (PPARβ), PGJ2 and rosiglitazone (PPARγ) – increased PGF2α secretion but did not affect PGFS mRNA abundance. During pregnancy (days 10–12 and 14–16), PPARα and PPARγ ligands did not change PGF2α release, whereas PPARβ agonist augmented PGF2α release on days 14–16 of pregnancy. In addition, WY-14643 and l-165,041 increased PGFS mRNA level in both examined periods of pregnancy. PPARγ agonist (PGJ2) and antagonist (T0070907) enhanced PGFS mRNA abundance in the endometrium on days 10–12 and 14–16 of pregnancy, respectively. The results indicate that PPARs are involved in the production of PGF2α by porcine endometrium, and that the sensitivity of the endometrium to PPAR ligands depends on reproductive status of animals.

FAM3A is a target gene of peroxisome proliferator-activated receptor gamma

BackgroundTo date, the biological function of FAM3A, the first member of FAM3 gene family, remains unknown. We aimed to investigate whether the expression of FAM3A in liver cells is regulated by peroxisome proliferator-activated receptors (PPARs). Methods and resultsThe transcriptional activity of human and mouse FAM3A gene promoters was determined by luciferase reporter assay system. PPARγ agonist rosiglitazone induced FAM3A expression in primary cultured mouse hepatocytes and human HepG2 cells. PPARγ antagonism blocked rosiglitazone-induced FAM3A expression, whereas PPARγ overexpression stimulated FAM3A expression in HepG2 cells. In contrast, PPARα agonist fenofibrate or PPARβ agonist GW0742 failed to affect FAM3A expression in HepG2 cells. The transcriptional activities of human and mouse FAM3A promoters were markedly stimulated by PPARγ activation, but not by PPARα and PPARβ activation. Chromatin immunoprecipitation (ChIP) assay revealed a direct binding of PPARγ to the putative peroxisome proliferator response element (PPRE) located at −1258/−1246 in the human FAM3A promoter. Site-directed mutagenesis of this PPRE-like motif abolished PPARγ's stimulatory effect on the transcriptional activity of human FAM3A promoter. In vivo, oral rosiglitazone treatment upregulated FAM3A expression in the livers of C57BL/6 mice and db/db mice. Moreover, upregulation of FAM3A by PPARγ activation was correlated with increased level of phosphorylated Akt (pAkt) in liver cells. ConclusionsFAM3A as a novel target gene of PPARγ. Upregulation of FAM3A by PPARγ activation is correlated with increased pAkt level in liver cells. General significanceUpregulation of FAM3A might contribute to PPARγ's metabolic effects in the liver.

Role of peroxisome proliferator-activated receptor β agonist on angiogenesis in hindlimb ischemic diabetic rats

IntroductionStudies indicated that PPARβ agonists play a role in modulation of angiogenesis. In this study, we evaluated the effect of specific PPARβ agonist, GW0742, on angiogenesis and serum vascular endothelial growth factor (VEGF), VEGF receptor-2 (VEGFR-2), and nitrite concentrations in hindlimb ischemia in normal and diabetic rats. MethodsHindlimb ischemic rats were divided into four groups: control, diabetic, control, and diabetic treated with GW0742 (n=7 each). Diabetes was induced by injection of streptozotocin (55mg/kg, ip). GW0742 was injected 1day after surgery (1mg/kg, sc). After 21days, blood samples were taken, and gastrocnemius muscles were harvested for immunohistochemistry. ResultsGW0742 significantly increased serum nitrite and VEGFR-2 concentrations and VEGF-to-VEGFR-2 ratio in control and diabetic rats. Capillary density was lower in diabetic animals compared to the control, and GW0742 significantly restored the capillary density in the control and diabetic hindlimb ischemic rats. ConclusionPPARβ agonists restore skeletal muscle angiogenesis and can be considered for prevention and/or treatment of peripheral vascular complications in diabetic subjects.

Antihypertensive Effects of Peroxisome Proliferator-Activated Receptor-β Activation in Spontaneously Hypertensive Rats

Activation of nuclear hormone receptor peroxisome proliferator-activated receptor β/δ (PPARβ) has been shown to improve insulin resistance and plasma high-density lipoprotein levels, but nothing is known about its effects in genetic hypertension. We studied whether the PPARβ agonist GW0742 might exert antihypertensive effects in spontaneously hypertensive rats (SHRs). The rats were divided into 4 groups, Wistar Kyoto rat-control, Wistar Kyoto rat-treated (GW0742, 5 mg · kg(-1) · day(-1) by oral gavage), SHR-control, and SHR-treated, and followed for 5 weeks. GW0742 induced a progressive reduction in systolic arterial blood pressure and heart rate in SHRs and reduced the mesenteric arterial remodeling, the increased aortic vasoconstriction to angiotensin II, and the endothelial dysfunction characteristic of SHRs. These effects were accompanied by a significant increase in endothelial NO synthase activity attributed to upregulated endothelial NO synthase and downregulated caveolin 1 protein expression. Moreover, GW0742 inhibited vascular superoxide production, downregulated p22(phox) and p47(phox) proteins, decreased both basal and angiotensin II-stimulated NADPH oxidase activity, inhibited extracellular-regulated kinase 1/2 activation, and reduced the expression of the proinflammatory and proatherogenic genes, interleukin 1β, interleukin 6, or intercellular adhesion molecule 1. None of these effects were observed in Wistar Kyoto rats. PPARβ activation, both in vitro and in vivo, increased the expression of the regulators of G protein-coupled signaling proteins RGS4 and RGS5, which negatively modulated the vascular actions of angiotensin II. PPARβ activation exerted antihypertensive effects, restored the vascular structure and function, and reduced the oxidative, proinflammatory, and proatherogenic status of SHRs. We propose PPARβ as a new therapeutic target in hypertension.

Expression of fatty acid binding proteins 3 and 5 genes in rat pancreatic islets and INS-1E cells: Regulation by fatty acids and glucose

Fatty acids binding proteins (FABPs) are involved in uptake, binding, transport and metabolism of fatty acids (FAs). Although FAs are known to stimulate insulin secretion from pancreatic islets when transiently elevated, while contributing to islet loss of function, lipotoxicity and apoptosis when chronically elevated, almost nothing is known regarding the FABPs in this tissue. The present study aimed at exploring the expression pattern and regulation of FABPs in rat islets and the insulin-secreting INS-1E cells. Rat islets and INS-1E cells expressed the heart/muscle type (FABP3) and the epidermal type (FABP5) genes. Different FAs significantly enhanced the expression of both FABPs. High glucose concentration induced a similar elevation of both FABP mRNA levels, and similarly to its effect on insulin 1 mRNA. Addition of oleic or palmitic acids to glucose did not render a further effect. FABP3 gene expression increased in response to PPARα agonist, while FABP5 increased in response to PPARα and PPARγ agonists, and decreased in response to a PPARβ agonist. Beta-oxidation of FAs is required for the gene expression of both FABP genes in INS-1E cells. Inhibition of CPT-1 by etomoxir inhibited the oleic acid-induced FABP 3 and 5 gene expression, while activation of AMPK by metformin amplified the oleic-induced expression of both FABPs. FABP3 and 5 gene transcription required de novo protein synthesis, since inhibition by cycloheximide significantly decreased both FABP mRNAs. These data show a complex interrelationship between glucose and FAs in the control of FABP gene expression and that FABP3 and 5 may play a role in insulin secretion.

Peroxisome Proliferator-Activated Receptor -β/δ, -γAgonists and Resveratrol Modulate Hypoxia Induced Changes in Nuclear Receptor Activators of Muscle Oxidative Metabolism

PPAR-α, PPAR-β, and PPAR-γ, and RXR in conjunction with PGC-1α and SIRT1, activate oxidative metabolism genes determining insulin sensitivity. In utero, hypoxia is commonly observed in Intrauterine Growth Restriction (IUGR), and reduced insulin sensitivity is often observed in these infants as adults. We sought to investigate how changes in oxygen tension might directly impact muscle PPAR regulation of oxidative genes. Following eight days in culture at 1% oxygen, C2C12 muscle myoblasts displayed a reduction of PGC-1α, PPAR-α, and RXR-α mRNA, as well as CPT-1b and UCP-2 mRNA. SIRT1 and PGC-1α protein was reduced, and PPAR-γ protein increased. The addition of a PPAR-β agonist (L165,041) for the final 24 hours of 1% treatment resulted in increased levels of UCP-2 mRNA and protein whereas Rosiglitazone induced SIRT1, PGC-1α, RXR-α, PPAR-α, CPT-1b, and UCP-2 mRNA and SIRT1 protein. Under hypoxia, Resveratrol induced SIRT1, RXR-α, PPAR-α mRNA, and PPAR-γ and UCP-2 protein. These findings demonstrate that hypoxia alters the components of the PPAR pathway involved in muscle fatty acid oxidative gene transcription and translation. These results have implications for understanding selective hypoxia adaptation and how it might impact long-term muscle oxidative metabolism and insulin sensitivity.