PPARδ Ligand Research Articles

Ginger extract prevents high-fat diet-induced obesity in mice via activation of the peroxisome proliferator-activated receptor δ pathway

The initiation of obesity entails an imbalance wherein energy intake exceeds expenditure. Obesity is increasing in prevalence and is now a worldwide health problem. Food-derived peroxisome proliferator-activated receptor δ (PPARδ) stimulators represent potential treatment options for obesity. Ginger (Zingiber officinale Roscoe) was previously shown to regulate the PPARγ signaling pathway in adipocytes. In this study, we investigated the antiobesity effects of ginger in vivo and the mechanism of action in vitro. Energy expenditure was increased, and diet-induced obesity was attenuated in C57BL/6J mice treated with dietary ginger extract (GE). GE also increased the number of Type I muscle fibers, improved running endurance capacity and upregulated PPARδ-targeted gene expression in skeletal muscle and the liver. 6-Shogaol and 6-gingerol acted as specific PPARδ ligands and stimulated PPARδ-dependent gene expression in cultured human skeletal muscle myotubes. An analysis of cellular respiration revealed that pretreating cultured skeletal muscle myotubes with GE increased palmitate-induced oxygen consumption rate, which suggested an increase in cellular fatty acid catabolism. These results demonstrated that sustained activation of the PPARδ pathway with GE attenuated diet-induced obesity and improved exercise endurance capacity by increasing skeletal muscle fat catabolism. 6-Shogaol and 6-gingerol may be responsible for the regulatory effects of dietary ginger on PPARδ signaling.

Activation of PPARδ: from computer modelling to biological effects.

PPARδ is a ligand-activated receptor that dimerizes with another nuclear receptor of the retinoic acid receptor family. The dimers interact with other co-activator proteins and form active complexes that bind to PPAR response elements and promote transcription of genes involved in lipid metabolism. It appears that various natural fatty acids and their metabolites serve as endogenous activators of PPARδ; however, there is no consensus in the literature on the nature of the prime activators of the receptor. In vitro and cell-based assays of PPARδ activation by fatty acids and their derivatives often produce conflicting results. The search for synthetic and selective PPARδ agonists, which may be pharmacologically useful, is intense. Current rational modelling used to obtain such compounds relies mostly on crystal structures of synthetic PPARδ ligands with the recombinant ligand binding domain (LBD) of the receptor. Here, we introduce an original computational prediction model for ligand binding to PPARδ LBD. The model was built based on EC50 data of 16 ligands with available crystal structures and validated by calculating binding probabilities of 82 different natural and synthetic compounds from the literature. These compounds were independently tested in cell-free and cell-based assays for their capacity to bind or activate PPARδ, leading to prediction accuracy of between 70% and 93% (depending on ligand type). This new computational tool could therefore be used in the search for natural and synthetic agonists of the receptor.

Activation of Peroxisome Proliferator-Activated Receptor δ Inhibits Angiotensin II-Induced Activation of Matrix Metalloproteinase-2 in Vascular Smooth Muscle Cells

We investigated the role of peroxisome proliferator-activated receptor (PPAR) δ on angiotensin (Ang) II-induced activation of matrix metalloproteinase (MMP)-2 in vascular smooth muscle cells (VSMCs). Activation of PPARδ by GW501516, a specific ligand for PPARδ, attenuated Ang II-induced activation of MMP-2 in a concentration-dependent manner. GW501516 also inhibited the generation of reactive oxygen species in VSMCs treated with Ang II. A marked increase in the mRNA levels of tissue inhibitor of metalloproteinase (TIMP)-2 and -3, endogenous antagonists of MMPs, was also observed in GW501516-treated VSMCs. These effects were markedly reduced in the presence of siRNAs against PPARδ, indicating that the effects of GW501516 are PPARδ dependent. Among the protein kinases inhibited by GW501516, suppression of phosphatidylinositol 3-kinase/Akt signaling was shown to have the greatest effect on activation of MMP-2 in VSMCs treated with Ang II. Concomitantly, GW501516-mediated inhibition of MMP-2 activation in VSMCs treated with Ang II was associated with the suppression of cell migration to levels approaching those in cells not exposed to Ang II. Thus, activation of PPARδ confers resistance to Ang II-induced degradation of the extracellular matrix by upregulating expression of its endogenous inhibitor TIMP and thereby modulating cellular responses to Ang II in vascular cells.

Abstract W P359: Activation of Prostacyclin Receptor (IP) in Human Brain Microvascular Endothelial Cells Stimulates Production of SAPPa

Previous studies have established that cerebral blood vessels possess high capacity to synthesize prostacyclin (PGI 2 ). Substantial evidence indicates that amyloid precursor protein (APP) and soluble APPα (sAPPα) have neurotrophic and nueroprotective properties. We hypothesized that activation of IP-cAMP pathway stimulates non-amyloidogenic processing of APP in cerebral endothelial cells. Western blotting was used to detect protein expression; real time RT-PCR was employed to measure mRNA levels of APP, and a disintegrin and metalloprotease 10 (ADAM10, an α processing enzyme); sAPPα secretion was detected in condition medium derived from culturing human brain microvascular endothelial cells (BMVECs), by ELISA. After human BMVECs were treated with PGI 2 analog iloprost (0.01, 0.05, 0.1, or 0.5 μM) for 3 days, protein levels of ADAM10 (n=7-9, P<0.05) and APP (n=6, P<0.05) were significantly increased in a concentration dependent manner, while β amyloidogenic processing enzyme BACE1, and other α processing enzymes such as ADAM9 and ADAM17 were not changed. mRNA levels of APP (n=7, P<0.05) and ADAM10 (n=4, P<0.05), as well as sAPPα production in human BMVECs (n=6, P<0.05) were also significantly augmented in response to iloprost treatment. Moreover, stimulation of human BMVECs with forskolin (40μM) significantly enhanced APP and ADAM10 protein expression. Most notably, iloprost significantly augmented protein expression of peroxisome proliferation-activated receptor-δ (PPARδ) and SIRT1. We further explored the role of PPARδ in APP processing. ADAM10 expression (n=6, P<0.05), but not APP and BACE1, was significantly increased in human BMVECs treated with PPARδ ligand GW501516 (30 or 100 nM). GW501516 (100 nM) also significantly increase sAPPα production (n=9-10, P<0.05). siRNA against PPARδ significantly suppressed basal levels of ADAM10, and blocked iloprost-induced ADAM10 expression (n=4, P<0.05). These findings suggest that activation of IP-cAMP pathway enhances non-amyloidogenic processing of APP and consequently increases production of neurotrophic molecule sAPPα in human BMVECs. Activation of PPARδ in part mediates iloprost-induced α processing of APP.

Desnutrin/ATGL Activates PPARδ to Promote Mitochondrial Function for Insulin Secretion in Islet β Cells

Excessive caloric intake leading to obesity is associated with insulin resistance and dysfunction of islet β cells. High-fat feeding decreases desnutrin (also called ATGL/PNPLA2) levels in islets. Here we show that desnutrin ablation via RIP-Cre (βKO) or RIP-CreER results in hyperglycemia with impaired glucose-stimulated insulin secretion (GSIS). Due to decreased lipolysis, islets have higher TAG content but lower free FA levels. βKO islets exhibit impaired mitochondrial respiration and lower production of ATP required for GSIS, along with decreased expression of PPARδ target genes involved in mitochondrial oxidation. Furthermore, synthetic PPARδ, but not PPARα, agonist restores GSIS and expression of mitochondrial oxidative genes in βKO mice, revealing that desnutrin-catalyzed lipolysis generates PPARδ ligands. Finally, adenoviral expression of desnutrin in βKO islets restores all defects of βKO islet phenotype and function, including GSIS and mitochondrial defects, demonstrating the critical role of the desnutrin-PPARδ-mitochondrial oxidation axis in regulating islet β cell GSIS.

Peroxisome proliferator acivated receptor δ (PPAR δ) activation enhances the development of cryopreserved embryos

Prostacyclin analog, iloprost, enhances the hatching, implantation, and live birth of mouse embryos (Huang et al, 2003, 2004). The enhancements are likely mediated via PPARδ, a nuclear receptor (Kang et al, 2011). L165041, a PPARδ ligand, mimics the effects of iloprost on fresh mouse embryos (Huang et al, 2007a, b). In this report we determine the effect of L165041 on the development of post-thaw embryos.

PPARδ induces estrogen receptor-positive mammary neoplasia through an inflammatory and metabolic phenotype linked to mTOR activation.

The peroxisome proliferator-activated receptor-δ (PPARδ) regulates a multitude of physiological processes associated with glucose and lipid metabolism, inflammation, and proliferation. One or more of these processes are potential risk factors for the ability of PPARδ agonists to promote tumorigenesis in the mammary gland. In this study, we describe a new transgenic mouse model in which activation of PPARδ in the mammary epithelium by endogenous or synthetic ligands resulted in progressive histopathologic changes that culminated in the appearance of estrogen receptor- and progesterone receptor-positive and ErbB2-negative infiltrating ductal carcinomas. Multiparous mice presented with mammary carcinomas after a latency of 12 months, and administration of the PPARδ ligand GW501516 reduced tumor latency to 5 months. Histopathologic changes occurred concurrently with an increase in an inflammatory, invasive, metabolic, and proliferative gene signature, including expression of the trophoblast gene, Plac1, beginning 1 week after GW501516 treatment, and remained elevated throughout tumorigenesis. The appearance of malignant changes correlated with a pronounced increase in phosphatidylcholine and lysophosphatidic acid metabolites, which coincided with activation of Akt and mTOR signaling that were attenuated by treatment with the mTOR inhibitor everolimus. Our findings are the first to show a direct role of PPARδ in the pathogenesis of mammary tumorigenesis, and suggest a rationale for therapeutic approaches to prevent and treat this disease.

Abstract 1385: PPARδ promotes mammary tumorigenesis through mTOR activation.

Abstract Background: Peroxisome proliferator-activated receptorδ (PPARδ) regulates a multitude of physiological processes associated with glucose and lipid metabolism, inflammation and proliferation. One or more of these processes are potential risk factors for the ability of PPARδ agonists to promote tumorigenesis in the mammary gland. In the present study, we describe a new transgenic mouse model in which activation of PPARδ by endogenous or synthetic ligands results in mammary neoplasia. Methods: Transgenic mice were generated in which expression of PPARδ was directed to the mammary gland under the control of the MMTV long terminal repeat. Results: Multiparous MMTV-PPARδ mice presented with infiltrating ductal carcinomas after a latency of 12 months. When transgenic animals were maintained on a diet supplemented with the PPARδ ligand GW501516, rapid progression to ductal and alveolar hyperplasia, dysplasia and ductal carcinoma in situ occurred within three months, and multifocal ductal carcinomas occurred after 5 months. Histopathological changes occurred in concert with a marked increase in phosphatidylcholine (PC) and lysoPC levels. Gene array profiling revealed an inflammatory, invasive, metabolic and proliferative signature denoted by enhanced expression of Saa1/2, S100a8, Klk6/7, Acsl4 and Plac1, and increased mTOR signaling. Treatment with the mTOR inhibitor, everolimus, dramatically reversed many of the histopathological and gene expression abnormalities. Conclusion: MMTV-PPARδ mice demonstrate a direct role for PPARδ in breast tumorigenesis that is linked to several previously unknown signaling processes. These findings suggest a rationale for new therapeutic approaches to prevent and treat this disease. Supported by 1N01CN43302-WA19 and 1P30CA51008 1st Choice Category: TB1 Cell Culture and Animal Models of Cancer Citation Format: Robert I. Glazer, Hongyan Yuan, Geeta Upadhyay, Yuzhi Yin, Levy Kopelovich. PPARδ promotes mammary tumorigenesis through mTOR activation. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1385. doi:10.1158/1538-7445.AM2013-1385

The biology of nematode- and IL4Rα-dependent murine macrophage polarization in vivo as defined by RNA-Seq and targeted lipidomics

AbstractAlternatively activated macrophages (AAMφ) are a major component of the response to helminth infection; however, their functions remain poorly defined. To better understand the helminth-induced AAMφ phenotype, we performed a systems-level analysis of in vivo derived AAMφ using an established mouse model. With next-generation RNA sequencing, we characterized the transcriptomes of peritoneal macrophages from BALB/c and IL4Rα−/− mice elicited by the nematode Brugia malayi, or via intraperitoneal thioglycollate injection. We defined expression profiles of AAMφ-associated cytokines, chemokines, and their receptors, providing evidence that AAMφ contribute toward recruitment and maintenance of eosinophilia. Pathway analysis highlighted complement as a potential AAMφ-effector function. Up-regulated mitochondrial genes support in vitro evidence associating mitochondrial metabolism with alternative activation. We mapped macrophage transcription start sites, defining over-represented cis-regulatory motifs within AAMφ-associated promoters. These included the binding site for PPAR transcription factors, which maintain mitochondrial metabolism. Surprisingly PPARγ, implicated in the maintenance of AAMφ, was down-regulated on infection. PPARδ expression, however, was maintained. To explain how PPAR-mediated transcriptional activation could be maintained, we used lipidomics to quantify AAMφ-derived eicosanoids, potential PPAR ligands. We identified the PPARδ ligand PGI2 as the most abundant AAMφ-derived eicosanoid and propose a PGI2-PPARδ axis maintains AAMφ during B malayi implantation.

ChemInform Abstract: Discovery, Design and Synthesis of Y‐Shaped Peroxisome Proliferator‐Activated Receptor δ Agonists as Potent anti‐Obesity Agents in vivo.

AbstractNovel Y‐shaped PPARδ ligands are synthesized by combination of a known ligand and a marine natural product using automatic docking experiments.

Activation of PPARδ prevents endothelial dysfunction induced by overexpression of amyloid-β precursor protein

Existing evidence suggests that amyloid-β precursor protein (APP) causes endothelial dysfunction and contributes to pathogenesis of atherosclerosis. In the present study, experiments were designed to: (1) determine the mechanisms underlying endothelial dysfunction and (2) define the effects of peroxisome proliferator-activated receptor delta (PPARδ) ligand on endothelial function in transgenic Tg2576 mice overexpressing mutated human APP. Confocal microscopy and western blot analyses of wild-type mice aortas provided evidence that APP protein is mainly present in endothelial cells. Overexpression of APP significantly impaired endothelium-dependent relaxations to acetylcholine and phosphorylation of endothelial nitric oxide synthase at Ser(1177) in aortas. HPLC analysis revealed that tetrahydrobiopterin (BH(4)) levels were reduced in Tg2576 mice aortas. This was caused by increased oxidation of BH(4) and reduced expression and activity of GTP-cyclohydrolase I. Furthermore, gp91phox protein expression and superoxide anion production were increased in aortas of Tg2576 mice. This augmented superoxide formation was completely prevented by the NADPH oxidase inhibitor VAS2870. Expression of copper-/zinc-superoxide dismutase (Cu/ZnSOD) and extracellular SOD was downregulated. Treatment with PPARδ ligand GW501516 (2 mg/kg/day) for 14 days significantly increased BH(4) bioavailability and improved endothelium-dependent relaxations in Tg2576 mice aortas. GW501516 also normalized protein expression of gp91(phox) and SODs, thereby reducing production of superoxide anion in the aortas. Our results suggest that in APP transgenic mice loss of nitric oxide and increased oxidative stress are the major causes of endothelial dysfunction. The vascular protective effects of GW501516 in Tg2576 mice appear to be critically dependent on prevention of superoxide anion production.

Structural Insights into Human Peroxisome Proliferator Activated Receptor Delta (PPAR-Delta) Selective Ligand Binding

Peroxisome proliferator activated receptors (PPARs δ, α and γ) are closely related transcription factors that exert distinct effects on fatty acid and glucose metabolism, cardiac disease, inflammatory response and other processes. Several groups developed PPAR subtype specific modulators to trigger desirable effects of particular PPARs without harmful side effects associated with activation of other subtypes. Presently, however, many compounds that bind to one of the PPARs cross-react with others and rational strategies to obtain highly selective PPAR modulators are far from clear. GW0742 is a synthetic ligand that binds PPARδ more than 300-fold more tightly than PPARα or PPARγ but the structural basis of PPARδ:GW0742 interactions and reasons for strong selectivity are not clear. Here we report the crystal structure of the PPARδ:GW0742 complex. Comparisons of the PPARδ:GW0742 complex with published structures of PPARs in complex with α and γ selective agonists and pan agonists suggests that two residues (Val312 and Ile328) in the buried hormone binding pocket play special roles in PPARδ selective binding and experimental and computational analysis of effects of mutations in these residues confirms this and suggests that bulky substituents that line the PPARα and γ ligand binding pockets as structural barriers for GW0742 binding. This analysis suggests general strategies for selective PPARδ ligand design.

Activation of PPARδ counteracts angiotensin II-induced ROS generation by inhibiting rac1 translocation in vascular smooth muscle cells

Angiotensin II (Ang II)-mediated modification of the redox milieu of vascular smooth muscle cells (VSMCs) has been implicated in several pathophysiological processes, including cell proliferation, migration and differentiation. In this study, we demonstrate that the peroxisome proliferator-activated receptor (PPAR) δ counteracts Ang II-induced production of reactive oxygen species (ROS) in VSMCs. Activation of PPARδ by GW501516, a specific ligand for PPARδ, significantly reduced Ang II-induced ROS generation in VSMCs. This effect was, however, reversed in the presence of small interfering (si)RNA against PPARδ. The marked increase in ROS levels induced by Ang II was also eliminated by the inhibition of phosphatidylinositol 3-kinase (PI3K) but not of protein kinase C, suggesting the involvement of the PI3K/Akt signalling pathway in this process. Accordingly, ablation of Akt with siRNA further enhanced the inhibitory effects of GW501516 in Ang II-induced superoxide production. Ligand-activated PPARδ also blocked Ang II-induced translocation of Rac1 to the cell membrane, inhibiting the activation of NADPH oxidases and consequently ROS generation. These results indicate that ligand-activated PPARδ plays an important role in the cellular response to oxidative stress by decreasing ROS generated by Ang II in vascular cells.

Abstract 2746: Thiazolidinediones augment anticancer effects of gemcitabine on human pancreatic cancer cells through PPARδ activation

Abstract In order to improve the prognosis of patients with unresectable pancreatic cancer, there is an urgent need for enhancement of the anticancer effect of gemcitabine (Gem), a first-line drug for the disease. Here, we demonstrated that ligands for peroxisome proliferator-activated receptor ≤ (PPARδ) such as pioglitazone (Pio) and rosiglitazone potentiated the cytotoxic action of Gem on human pancreatic cancer cells in a dosage-dependent manner. Notably, the synergistic effect was PPARδ-dependent, since the effect was augmented by PPARδ overexpression and was attenuated by both a PPARδ inhibitor (GW9662) and PPARδ-specific siRNA. To further increase the collaborative effect, the histone deacetylase (HDAC) inhibitor valproic acid (VPA), a known potentiator for PPARδ function, was added to the combinatorial treatment, robustly inducing apoptosis mediated by highly expressed death receptors, including Fas/CD95 and DR5. In xenograft tumor experiments in nude mice, Gem plus Pio significantly suppressed tumor growth as compared with the control treatment, while Gem-only treatment did not. Triple treatment with Gem, Pio, and VPA failed to demonstrate a significant antitumor effect when compared with Gem plus Pio in the current setting. Considered together, Gem plus PPARδ ligands, including Pio, may have therapeutic advantage in the treatment of advanced pancreatic cancer. Since Pio is widely used in the treatment of diabetes mellitus, it may become a feasible partner of Gem-based chemotherapy, fine-tuning the strength of the therapy in a dosage-dependent fashion. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2746. doi:1538-7445.AM2012-2746

The PPARδ ligand L‐165041 inhibits vegf‐induced angiogenesis, but the antiangiogenic effect is not related to PPARδ

Peroxisome proliferator-activated receptor (PPAR)δ is known to be expressed ubiquitously and involved in lipid and glucose metabolism. Recent studies have demonstrated that PPARδ is expressed in endothelial cells (ECs) and plays a potential role in endothelial survival and proliferation. Although PPARα and PPARγ are well recognized to play anti-inflammatory, antiproliferative, and antiangiogenic roles in ECs, the general effect of PPARδ on angiogenesis in ECs remains unclear. Thus, we investigated the effect of the PPARδ ligand L-165041 on vascular EC proliferation and angiogenesis in vitro as well as in vivo. Our data show that L-165041 inhibited VEGF-induced cell proliferation and migration in human umbilical vein ECs (HUVECs). L-165041 also inhibited angiogenesis in the Matrigel plug assay and aortic ring assay. Flow cytometric analysis indicated that L-165041 reduced the number of ECs in the S phase and the expression levels of cell cycle regulatory proteins such as cyclin A, cyclin E, CDK2, and CDK4; phosphorylation of the retinoblastoma protein was suppressed by pretreatment with L-165041. We confirmed whether these antiangiogenic effects of L-165041 were PPARδ-dependent using GW501516 and PPARδ siRNA. GW501516 treatment did not inhibit VEGF-induced angiogenesis, and transfection of PPARδ siRNA did not reverse this antiangiogenic effect of L-165041, suggesting that the antiangiogenic effect of L-165041 on ECs is PPARδ-independent. Together, these data indicate that the PPARδ ligand L-165041 inhibits VEGF-stimulated angiogenesis by suppressing the cell cycle progression independently of PPARδ. This study highlights the therapeutic potential of L-165041 in the treatment of many disorders related to pathological angiogenesis.

Discovery, design and synthesis of Y-shaped peroxisome proliferator-activated receptor δ agonists as potent anti-obesity agents in vivo

We have discovered and demonstrated the in vitro and in vivo PPARδ-selective activity of novel Y-shaped agonists. These compounds activated hPPARδ with EC50 values between 1 and 523 nM. Surprisingly, compounds 10a, 11d, 11e and 11f were the most potent and most selective hPPARδ agonists with 104-fold selectivity over the other two subtypes, namely, hPPARα and hPPARγ. The PPARδ ligands 10a, 11e and 11f showed good bioavailability and in vivo efficacy.

Advanced QSAR studies on PPARδ ligands related to metabolic diseases

PPARδ is a nuclear receptor that, when activated, regulates the metabolism of carbohydrates and lipids and is related to metabolic syndrome and type 2 diabetes. To understand the main interactions between ligands and PPARδ, we have constructed 2D and 3D QSAR models and compared them with HOMO, LUMO and electrostatic potential maps of the compounds studied, as well as docking results. All QSAR models showed good statistical parameters and prediction outcomes. The QSAR models were used to predict the biological activity of an external test set, and the predicted values are in good agreement with the experimental results. Furthermore, we employed all maps to evaluate the possible interactions between the ligands and PPARδ. These predictive QSAR models, along with the HOMO, LUMO and MEP maps, can provide insights into the structural and chemical properties that are needed in the design of new PPARδ ligands that have improved biological activity and can be employed to treat metabolic diseases.

PPARδ Coordinates Angiotensin II-induced Senescence in Vascular Smooth Muscle Cells through PTEN-mediated Inhibition of Superoxide Generation

Cellular senescence-associated changes in blood vessels have been implicated in aging and age-related cardiovascular disorders. Here, we demonstrate that peroxisome proliferator-activated receptor (PPAR) δ coordinates angiotensin (Ang) II-induced senescence of human vascular smooth muscle cells (VSMCs). Activation of PPARδ by GW501516, a specific ligand for PPARδ, significantly attenuated Ang II-induced generation of superoxides and suppressed senescence of VSMCs. A marked increase in the levels of p53 and p21 induced by Ang II was blunted by the treatment with GW501516. Ligand-activated PPARδ up-regulated expression of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and suppressed the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. Knockdown of PTEN with siRNA abrogated the effects of PPARδ on cellular senescence, on PI3K/Akt signaling, and on generation of ROS in VSMCs treated with Ang II. Finally, administration of GW501516 to apoE-deficient mice treated with Ang II significantly reduced the number of senescent cells in the aorta, where up-regulation of PTEN with reduced levels of phosphorylated Akt and ROS was demonstrated. Thus, ligand-activated PPARδ confers resistance to Ang II-induced senescence by up-regulation of PTEN and ensuing modulation of the PI3K/Akt signaling to reduce ROS generation in vascular cells.

Role of Lipid Peroxidation and PPAR-δ in Amplifying Glucose-Stimulated Insulin Secretion

OBJECTIVEPrevious studies show that polyunsaturated fatty acids (PUFAs) increase the insulin secretory capacity of pancreatic β-cells. We aimed at identifying PUFA-derived mediators and their cellular targets that are involved in the amplification of insulin release from β-cells preexposed to high glucose levels.RESEARCH DESIGN AND METHODSThe content of fatty acids in phospholipids of INS-1E β-cells was determined by lipidomics analysis. High-performance liquid chromatography was used to identify peroxidation products in β-cell cultures. Static and dynamic glucose-stimulated insulin secretion (GSIS) assays were performed on isolated rat islets and/or INS-1E cells. The function of peroxisome proliferator–activated receptor-δ (PPAR-δ) in regulating insulin secretion was investigated using pharmacological agents and gene expression manipulations.RESULTSHigh glucose activated cPLA2 and, subsequently, the hydrolysis of arachidonic and linoleic acid (AA and LA, respectively) from phospholipids in INS-1E cells. Glucose also increased the level of reactive oxygen species, which promoted the peroxidation of these PUFAs to generate 4-hydroxy-2E-nonenal (4-HNE). The latter mimicked the GSIS-amplifying effect of high glucose preexposure and of the PPAR-δ agonist GW501516 in INS-1E cells and isolated rat islets. These effects were blocked with GSK0660, a selective PPAR-δ antagonist, and the antioxidant N-acetylcysteine or by silencing PPAR-δ expression. High glucose, 4-HNE, and GW501516 also induced luciferase expression in a PPAR-δ–mediated transactivation assay. Cytotoxic effects of 4-HNE were observed only above the physiologically effective concentration range.CONCLUSIONSElevated glucose levels augment the release of AA and LA from phospholipids and their peroxidation to 4-HNE in β-cells. This molecule is an endogenous ligand for PPAR-δ, which amplifies insulin secretion in β-cells.

Immunomodulatory action of dietary fish oil and targeted deletion of intestinal epithelial cell PPARδ in inflammation-induced colon carcinogenesis

The ligand-activated transcription factor peroxisome proliferator-activated receptor (PPAR)-δ is highly expressed in colonic epithelial cells; however, the role of PPARδ ligands, such as fatty acids, in mucosal inflammation and malignant transformation has not been clarified. Recent evidence suggests that the anti-inflammatory/chemoprotective properties of fish oil (FO)-derived n-3 polyunsaturated fatty acids (PUFAs) may be partly mediated by PPARδ. Therefore, we assessed the role of PPARδ in modulating the effects of dietary n-3 PUFAs by targeted deletion of intestinal epithelial cell PPARδ (PPARδ(ΔIEpC)). Subsequently, we documented changes in colon tumorigenesis and the inflammatory microenvironment, i.e., local [mesenteric lymph node (MLN)] and systemic (spleen) T cell activation. Animals were fed chemopromotive [corn oil (CO)] or chemoprotective (FO) diets during the induction of chronic inflammation/carcinogenesis. Tumor incidence was similar in control and PPARδ(ΔIEpC) mice. FO reduced mucosal injury, tumor incidence, colonic STAT3 activation, and inflammatory cytokine gene expression, independent of PPARδ genotype. CD8(+) T cell recruitment into MLNs was suppressed in PPARδ(ΔIEpC) mice. Similarly, FO reduced CD8(+) T cell numbers in the MLN. Dietary FO independently modulated MLN CD4(+) T cell activation status by decreasing CD44 expression. CD11a expression by MLN CD4(+) T cells was downregulated in PPARδ(ΔIEpC) mice. Lastly, splenic CD62L expression was downregulated in PPARδ(ΔIEpC) CD4(+) and CD8(+) T cells. These data demonstrate that expression of intestinal epithelial cell PPARδ does not influence azoxymethane/dextran sodium sulfate-induced colon tumor incidence. Moreover, we provide new evidence that dietary n-3 PUFAs attenuate intestinal inflammation in an intestinal epithelial cell PPARδ-independent manner.