PPARδ Activation Research Articles

Peroxisome proliferator‐activated receptor β/δ (PPARβ/δ) is highly expressed in liposarcoma and promotes migration and proliferation

Aberrations of specialized metabolic pathways might be implicated in the development of neoplasias. Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors with important functions in metabolism. PPARβ/δ and PPARγ act in the proliferation and differentiation of adipose tissue progenitor cells. Thus, a potential use of PPARγ agonists for the treatment of liposarcoma had been suggested, but clinical trials failed to detect beneficial effects. We show here that PPARδ is highly expressed in liposarcoma compared to lipoma and correlates with proliferation. Stimulation of liposarcoma cell lines with a specific PPARδ agonist increases proliferation, which is abolished by a PPARδ-siRNA or a specific PPARδ antagonist. Expression of the adipose tissue secretory factor leptin is lower in liposarcoma compared to lipoma and leptin reduces proliferation of liposarcoma cell lines. PPARδ activation stimulates cell migration whereas leptin diminishes it. We demonstrate that PPARδ directly represses leptin as: (a) leptin becomes down-regulated upon PPARδ activation; (b) PPARδ represses leptin promoter activity in different sarcoma cell lines; (c) deletion of a PPAR/RxR binding element in the leptin promoter abolishes repression by PPARδ; and (d) in chromatin immunoprecipitation we confirm in vivo binding of PPARδ to the leptin promoter. Our data suggest inhibition of PPARδ as a potential novel strategy to reduce liposarcoma cell proliferation.

β-Catenin and p120 Mediate PPARδ-Dependent Proliferation Induced by Helicobacter pylori in Human and Rodent Epithelia

Colonization of gastric mucosa by Helicobacter pylori leads to epithelial hyperproliferation, which increases the risk for gastric adenocarcinoma. One H pylori virulence locus associated with cancer risk, cag, encodes a secretion system that transports effectors into host cells and leads to aberrant activation of β-catenin and p120-catenin (p120). Peroxisome proliferator-activated receptor (PPAR)δ is a ligand-activated transcription factor that affects oncogenesis in conjunction with β-catenin. We used a carcinogenic H pylori strain to define the role of microbial virulence constituents and PPARδ in regulating epithelial responses that mediate development of adenocarcinoma. Gastric epithelial cells or colonies were co-cultured with the H pylori cag(+) strain 7.13 or cagE(-), cagA(-), soluble lytic transglycosylase(-), or cagA(-)/soluble lytic transglycosylase(-) mutants. Levels of PPARδ and cyclin E1 were determined by real-time, reverse-transcription polymerase chain reaction, immunoblot analysis, or immunofluorescence microscopy; proliferation was measured in 3-dimensional culture. PPARδ and Ki67 expression were determined by immunohistochemical analysis of human biopsies and rodent gastric mucosa. H pylori induced β-catenin- and p120-dependent expression and activation of PPARδ in gastric epithelial cells, which were mediated by the cag secretion system substrates CagA and peptidoglycan. H pylori stimulated proliferation in vitro, which required PPARδ-mediated activation of cyclin E1; H pylori did not induce expression of cyclin E1 in a genetic model of PPARδ deficiency. PPARδ expression and proliferation in rodent and human gastric tissue was selectively induced by cag(+) strains and PPARδ levels normalized after eradication of H pylori. The H pylori cag secretion system activates β-catenin, p120, and PPARδ, which promote gastric epithelial cell proliferation via activation of cyclin E1. PPARδ might contribute to gastric adenocarcinoma development in humans.

Activation of peroxisome proliferators-activated receptor (PPAR ) promotes blastocyst hatching in mice

Prostaglandins participate in a variety of female reproductive processes, including ovulation, fertilization, embryo implantation and parturition. In particular, maternal prostacyclin (PGI(2)) is critical for embryo implantation and the action of PGI(2) is not mediated via its G-protein-coupled membrane receptor, IP, but its nuclear receptor, peroxisome-proliferator-activated receptor δ (PPARδ). Recently, several studies have shown that PGI(2) enhances blastocyst development and/or hatching rate in vitro, and subsequently implantation and live birth rates in mice. However, the mechanism by which PGI(2) improves preimplantation embryo development in vitro remains unclear. Using molecular, pharmacologic and genetic approaches, we show that PGI(2)-induced PPARδ activation accelerates blastocyst hatching in mice. mRNAs for PPARδ, retinoid X receptor (heterodimeric partners of PPARδ) and PGI(2) synthase (PGIS) are temporally induced after zygotic gene activation, and their expression reaches maximum levels at the blastocyst stage, suggesting that functional complex of PPARδ can be formed in the blastocyst. Carbaprostacyclin (a stable analogue of PGI(2)) and GW501516 (a PPARδ selective agonist) significantly accelerated blastocyst hatching but did not increase total cell number of cultured blastocysts. Whereas U51605 (a PGIS inhibitor) interfered with blastocyst hatching, GW501516 restored U51605-induced retarded hatching. In contrast to the improvement of blastocyst hatching by PPARδ agonists, PPAR antagonists significantly inhibited blastocyst hatching. Furthermore, deletion of PPARδ at early stages of preimplantation mouse embryos caused delay of blastocyst hatching, but did not impair blastocyst development. Taken together, PGI(2)-induced PPARδ activation accelerates blastocyst hatching in mice.

Glycogen depletion increases peroxisome proliferator activated receptor‐δ (PPAR‐δ) activity following acute exercise

Performing exercise with low muscle glycogen has profound effects on substrate utilization and gene transcription. The aim of the present study was to examine signaling pathways potentially responsible for modulating gene transcription during exercise in a glycogen-depleted state. Methods Twenty female Wistar rats were randomly assigned to 5 experimental groups: control [CON]; normal glycogen control [NG-C]; normal glycogen exercise [NG-E]; low glycogen control [LG-C]; and low glycogen exercise [LG-E]). Results Exercise reduced muscle glycogen by 47 and 75% post exercise in the NG-E and LG-E groups respectively. The exercise protocol meant that the LG-E group began exercise with a 40% decrease in resting glycogen levels (2.1 ± 0.1 to 1.3 ± 0.3 nmol.mg.wet wt; P<0.05). Exercise in low glycogen increased AMPK α1 activity by 32% (CON 0.04 ± 0.002, LG-E 0.06 ± 0.006 Units mg/AMPK; P<0.05) and AMPK α2 activity by 147% (CON 0.03 ± 0.004, LG-E 0.07 ± 0.005 Units mg/AMPK; P<0.05). In addition to the increase in AMPK activity, ChIP analysis demonstrated increased PPAR-δ binding to the CPT1 promoter in the LG-C, LG-E, and NG-E experimental groups compared to the CON group or the NG-C groups. Discussion Our data suggests that PPAR-δ activation may contribute to the altered gene transcription previously reported during exercise in a glycogen-depleted state.

Chronic AMPK activation induces beneficial phenotypic adaptations in mdx mouse skeletal muscle

A therapeutic approach for Duchenne muscular dystrophy (DMD) is to upregulate utrophin levels in skeletal muscle in an effort to compensate for the lack of dystrophin. We have previously hypothesized that promotion of the slow, oxidative myogenic program, which triggers utrophin upregulation, can attenuate the dystrophic pathology in mdx animals, the murine model of DMD. Indeed, treatment of mdx mice with the PPARδ activator GW501516 shifted muscle phenotype and ameliorated the disease pathology (Miura et al. Hum Mol Genet. 18:4640–49, 2009). Treatment of healthy mice with the AMPK activator AICAR enhances oxidative capacity and triggers a fast-to-slow fiber-type transition. Our purpose was to evaluate the effects of chronic AICAR administration on muscle gene expression and the dystrophic pathology in mdx mice. AICAR mitigated muscle pseudo-hypertrophy and attenuated central nucleation. Furthermore, we observed an elevation in mitochondrial enzyme activity, an increase in MHC IIa-positive fibers, and slower twitch contraction kinetics in the EDL muscle. Utrophin and PGC-1α proteins were augmented in response to AICAR, concomitant with a reduction in RIP140. Exercise increased utrophin A, PGC-1α, and PPARδ mRNAs. This effect was attenuated with AICAR. Our data suggest that AICAR-evoked muscle plasticity results in beneficial phenotypic adaptations in mdx mice. Supported by MDA (USA), CIHR and NSERC.

Transcriptional up-regulation of antioxidant genes by PPARδ inhibits angiotensin II-induced premature senescence in vascular smooth muscle cells

This study evaluated peroxisome proliferator-activated receptor (PPAR) δ as a potential target for therapeutic intervention in Ang II-induced senescence in human vascular smooth muscle cells (hVSMCs). Activation of PPARδ by GW501516, a specific agonist of PPARδ, significantly inhibited the Ang II-induced premature senescence of hVSMCs. Agonist-activated PPARδ suppressed the generation of Ang II-triggered reactive oxygen species (ROS) with a concomitant reduction in DNA damage. Notably, GW501516 up-regulated the expression of antioxidant genes, such as glutathione peroxidase 1, thioredoxin 1, manganese superoxide dismutase and heme oxygenase 1. siRNA-mediated down-regulation of these antioxidant genes almost completely abolished the effects of GW501516 on ROS production and premature senescence in hVSMCs treated with Ang II. Taken together, the enhanced transcription of antioxidant genes is responsible for the PPARδ-mediated inhibition of premature senescence through sequestration of ROS in hVSMCs treated with Ang II.

Activation of Peroxisome Proliferator–Activated Receptor δ Inhibits Streptozotocin-Induced Diabetic Nephropathy Through Anti-Inflammatory Mechanisms in Mice

OBJECTIVEActivation of the nuclear hormone receptor peroxisome proliferator–activated receptor (PPAR)-δ has been shown to improve insulin resistance, adiposity, and plasma HDL levels. Several studies have reported that activation of PPARδ is atheroprotective; however, the role of PPARδ in renal function remains unclear. Here, we report the renoprotective effects of PPARδ activation in a model of streptozotocin-induced diabetic nephropathy.RESEARCH DESIGN AND METHODSEight-week-old male C57BL/6 mice were divided into three groups: 1) nondiabetic control mice, 2) diabetic mice, and 3) diabetic mice treated with the PPARδ agonist GW0742 (1 mg/kg/day). GW0742 was administered by gavage for 8 weeks after inducing diabetes.RESULTSGW0742 decreased urinary albumin excretion without altering blood glucose levels. Macrophage infiltration, mesangial matrix accumulation, and type IV collagen deposition were substantially attenuated by GW0742. The gene expression of inflammatory mediators in the kidney cortex, such as monocyte chemoattractant protein-1 (MCP-1) and osteopontin (OPN), was also suppressed. In vitro studies demonstrated that PPARδ activation increased the expression of anti-inflammatory corepressor B-cell lymphoma-6, which subsequently suppressed MCP-1 and OPN expression.CONCLUSIONSThese findings uncover a previously unrecognized mechanism for the renoprotective effects of PPARδ agonists and support the concept that PPARδ agonists may offer a novel therapeutic approach for the treatment of diabetic nephropathy.

PPARδ activation acts cooperatively with 3-phosphoinositide-dependent protein kinase-1 to enhance mammary tumorigenesis.

Peroxisome proliferator-activated receptorδ (PPARδ) is a transcription factor that is associated with metabolic gene regulation and inflammation. It has been implicated in tumor promotion and in the regulation of 3-phosphoinositide-dependent kinase-1 (PDK1). PDK1 is a key regulator of the AGC protein kinase family, which includes the proto-oncogene AKT/PKB implicated in several malignancies, including breast cancer. To assess the role of PDK1 in mammary tumorigenesis and its interaction with PPARδ, transgenic mice were generated in which PDK1 was expressed in mammary epithelium under the control of the MMTV enhancer/promoter region. Transgene expression increased pT308AKT and pS9GSK3β, but did not alter phosphorylation of mTOR, 4EBP1, ribosomal protein S6 and PKCα. The transgenic mammary gland also expressed higher levels of PPARδ and a gene expression profile resembling wild-type mice maintained on a diet containing the PPARδ agonist, GW501516. Both wild-type and transgenic mice treated with GW501516 exhibited accelerated rates of tumor formation that were more pronounced in transgenic animals. GW501516 treatment was accompanied by a distinct metabolic gene expression and metabolomic signature that was not present in untreated animals. GW501516-treated transgenic mice expressed higher levels of fatty acid and phospholipid metabolites than treated wild-type mice, suggesting the involvement of PDK1 in enhancing PPARδ-driven energy metabolism. These results reveal that PPARδ activation elicits a distinct metabolic and metabolomic profile in tumors that is in part related to PDK1 and AKT signaling.

Vascular PPARδ Protects Against Stroke-Induced Brain Injury

To investigate the effects of peroxisome proliferator-activated receptor (PPAR)δ in the cerebral vasculature following stroke-induced brain injury. Here, we report a novel finding that selective PPARδ genetic deletion in vascular smooth muscle cells (VSMCs) resulted in increased cerebrovascular permeability and brain infarction in mice after middle cerebral artery occlusion (MCAO). Mechanistically, we revealed for the first time that PPARδ expression is reduced, but matrix metalloproteinase (MMP)-9 activity is increased in cultured VSMCs after oxygen-glucose deprivation and also in the cerebral cortex of mice following MCAO. Moreover, gain- and loss of PPARδ function in VSMCs significantly reduces and increases oxygen-glucose deprivation-induced MMP-9 activity, respectively. We have further identified that MMP-9 is a direct target of PPARδ-mediated transrepression by chromatin immunoprecipitation and PPARδ transcriptional activity assays. Furthermore, inhibition of MMP-9 activity by lentiviral MMP-9 short hairpin RNA effectively improves cerebrovascular permeability and reduces brain infarction in VSMC-selective PPARδ conditional knockout mice after MCAO. Our data demonstrate that PPARδ in VSMCs can prevent ischemic brain injury by inhibition of MMP-9 activation and attenuation of postischemic inflammation. The pharmacological activation of PPARδ may provide a new therapeutic strategy to treat stroke-induced vascular and neuronal damage.

Role of Peroxisome Proliferator-activated Receptor δ/β in Hepatic Metabolic Regulation

Pharmacological activation of peroxisome proliferator-activated receptor δ/β (PPARδ/β) improves glucose handling and insulin sensitivity. The target tissues of drug actions remain unclear. We demonstrate here that adenovirus-mediated liver-restricted PPARδ activation reduces fasting glucose levels in chow- and high fat-fed mice. This effect is accompanied by hepatic glycogen and lipid deposition as well as up-regulation of glucose utilization and de novo lipogenesis pathways. Promoter analyses indicate that PPARδ regulates hepatic metabolic programs through both direct and indirect transcriptional mechanisms partly mediated by its co-activator, PPARγ co-activator-1β. Assessment of the lipid composition reveals that PPARδ increases the production of monounsaturated fatty acids, which are PPAR activators, and reduces that of saturated FAs. Despite the increased lipid accumulation, adeno-PPARδ-infected livers exhibit less damage and show a reduction in JNK stress signaling, suggesting that PPARδ-regulated lipogenic program may protect against lipotoxicity. The altered substrate utilization by PPARδ also results in a secondary effect on AMP-activated protein kinase activation, which likely contributes to the glucose-lowering activity. Collectively, our data suggest that PPARδ controls hepatic energy substrate homeostasis by coordinated regulation of glucose and fatty acid metabolism, which provide a molecular basis for developing PPARδ agonists to manage hyperglycemia and insulin resistance.

The contrasting roles of PPARδ and PPARγ in regulating the metabolic switch between oxidation and storage of fats in white adipose tissue

BackgroundThe nuclear receptors peroxisome proliferator-activated receptor γ (PPARγ) and peroxisome proliferator-activated receptor δ (PPARδ) play central roles in regulating metabolism in adipose tissue, as well as being targets for the treatment of insulin resistance. While the role of PPARγ in regulating insulin sensitivity has been well defined, research into PPARδ has been limited until recently due to a scarcity of selective PPARδ agonists.ResultsThe metabolic effects of PPARγ and PPARδ activation have been examined in vivo in white adipose tissue from ob/ob mice and in vitro in cultured 3T3-L1 adipocytes using 1H nuclear magnetic resonance spectroscopy and mass spectrometry metabolomics to understand the receptors' contrasting roles. These steady state measurements were supplemented with 13C-stable isotope substrate labeling to assess fluxes, in addition to respirometry and transcriptomic microarray analysis. The metabolic effects of the receptors were readily distinguished, with PPARγ activation characterized by increased fat storage, synthesis and elongation, while PPARδ activation caused increased fatty acid β-oxidation, tricarboxylic acid cycle rate and oxidation of extracellular branch chain amino acids. Stimulated glycolysis and increased fatty acid desaturation were common pathways for the agonists.ConclusionsPPARγ and PPARδ restore insulin sensitivity through varying mechanisms. PPARδ activation increases total oxidative metabolism in white adipose tissue, a tissue not traditionally thought of as oxidative. However, the increased metabolism of branch chain amino acids may provide a mechanism for muscle atrophy, which has been linked to activation of this nuclear receptor. PPARδ has a role as an anti-obesity target and as an anti-diabetic, and hence may target both the cause and consequences of dyslipidemia.

The Myocyte Expression of Adiponectin Receptors and PPARδ Is Highly Coordinated and Reflects Lipid Metabolism of the Human Donors

Muscle lipid oxidation is stimulated by peroxisome proliferator-activated receptor (PPAR) δ or adiponectin receptor signalling. We studied human myocyte expression of the PPARδ and adiponectin receptor genes and their relationship to lipid parameters of the donors. The mRNA levels of the three adiponectin receptors, AdipoR1, AdipoR2, and T-cadherin, were highly interrelated (r ≥ 0.91). However, they were not associated with GPBAR1, an unrelated membrane receptor. In addition, the adiponectin receptors were positively associated with PPARδ expression (r ≥ 0.75). However, they were not associated with PPARα. Using stepwise multiple linear regression analysis, PPARδ was a significant determinant of T-cadherin (P = .0002). However, pharmacological PPARδ activation did not increase T-cadherin expression. The myocyte expression levels of AdipoR1 and T-cadherin were inversely associated with the donors' fasting plasma triglycerides (P < .03). In conclusion, myocyte expression of PPARδ and the adiponectin receptors are highly coordinated, and this might be of relevance for human lipid metabolism in vivo.

Regulation of ABCG1 expression in human keratinocytes and murine epidermis

ABCG1, a member of the ATP binding cassette superfamily, facilitates the efflux of cholesterol from cells to HDL. In this study, we demonstrate that ABCG1 is expressed in cultured human keratinocytes and murine epidermis, and induced during keratinocyte differentiation, with increased levels in the outer epidermis. ABCG1 is regulated by liver X receptor (LXR) and peroxisome proliferator-activated receptor-δ (PPAR-δ) activators, cellular sterol levels, and acute barrier disruption. Both LXR and PPAR-δ activators markedly stimulate ABCG1 expression in a dose- and time-dependent fashion. PPAR-γ activators also increase ABCG1 expression, but to a lesser degree. In contrast, activators of PPAR-α, retinoic acid receptor, retinoid X receptor, and vitamin D receptor do not alter ABCG1 expression. In response to increased intracellular sterol levels, ABCG1 expression increases, whereas inhibition of cholesterol biosynthesis decreases ABCG1 expression. In vivo, ABCG1 is stimulated 3-6 h after acute barrier disruption by either tape stripping or acetone treatment, an increase that can be inhibited by occlusion, suggesting a potential role of ABCG1 in permeability barrier homeostasis. Although Abcg1-null mice display normal epidermal permeability barrier function and gross morphology, abnormal lamellar body (LB) contents and secretion leading to impaired lamellar bilayer formation could be demonstrated by electron microscopy, indicating a potential role of ABCG1 in normal LB formation and secretion.

Expression and regulation of GPAT isoforms in cultured human keratinocytes and rodent epidermis

Phospholipids are required for epidermal lamellar body formation. Glycerol 3-phosphate acyltransferases (GPATs) catalyze the initial step in the biosynthesis of glycerolipids. Little is known about the expression and regulation of GPATs in epidermis/keratinocytes. Here, we demonstrate that GPAT 1, 3, and 4 are expressed in epidermis/keratinocytes, whereas GPAT2 is not detected. In mouse epidermis, GPAT 3 and 4 are mainly localized to the upper layers whereas GPAT1 is found in both the upper and lower layers. GPAT1 and 3 mRNA increase during fetal rat epidermal development. No change in GPAT expression was observed in adult mice following acute permeability barrier disruption. Calcium-induced human keratinocyte differentiation increased GPAT3 mRNA whereas both GPAT1 and 4 mRNA levels decreased. In parallel, total GPAT activity increased 2-fold in differentiated keratinocytes attributable to an increase in N-ethylmaleimide (NEM) sensitive GPAT activity localized to microsomes with little change in NEM resistant activity, consistent with an increase in GPAT3. Furthermore, PPARγ or PPARδ activators increased GPAT3 mRNA, microsomal GPAT activity, and glycerol lipid synthesis without affecting the expression of GPAT1 or 4. Finally, both PPARγ and PPARδ activators increased GPAT3 mRNA via increasing its transcription. Thus, multiple isoforms of GPAT are expressed and differentially regulated in epidermis/keratinocytes.

Peroxisome Proliferator-activated Receptor δ Activators Induce IL-8 Expression in Nonstimulated Endothelial Cells in a Transcriptional and Posttranscriptional Manner*

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that are implicated in the regulation of lipid and glucose homeostasis. PPAR agonists have been shown to control inflammatory processes, in part by inhibiting distinct proinflammatory genes (e.g. Il-1β and IFN-γ). IL-8 is a member of the proinflammatory chemokine family that is important for various functions, such as mediating the adhesion of eosinophilic granulocytes onto endothelial cells. The influence of PPARδ activators on the expression of IL-8 in noninduced quiescent endothelial cells is unclear. Therefore, we explored the influence of PPARδ activators on the expression of IL-8 in nonstimulated endothelial cells. PPARδ agonists induce IL-8 expression in human umbilical vein endothelial cells. This induction is demonstrated at the level of both protein and mRNA expression. Transcriptional activation studies using IL-8 reporter gene constructs and DNA binding assays revealed that PPARδ agonists mediated their effects via an NFκB binding site. It is well known that IL-8 is also regulated by mRNA stability. To provide further evidence for this concept, we performed mRNA stability assays and found that PPARδ agonists induce the mRNA stability of IL-8. In addition, we showed that PPARδ agonists induce the phosphorylation of ERK1/2 and p38, which are known to be involved in the increase of mRNA stability. The inhibition of these MAPK signaling pathways resulted in a significant suppression of the induced IL-8 expression and the reduced mRNA stability. Therefore, our data provide the first evidence that PPARδ induces IL-8 expression in nonstimulated endothelial cells via transcriptional as well as posttranscriptional mechanisms.

Peroxisome proliferator-activated receptor delta agonists attenuated the C-reactive protein-induced pro-inflammation in cardiomyocytes and H9c2 cardiomyoblasts

C-reactive protein (CRP) has emerged as a new marker for cardiovascular diseases. Activation of peroxisome proliferator-activated receptor δ (PPARδ) plays beneficial roles in cardiac disorders. However, the relationship between CRP and PPARδ in cardiac cells remains unclear. This study focused on the underlying molecular mechanisms of CRP and PPARδagonists. Cardiomyocytes and cardiomyoblast cell line (H9c2) were used in different groups: Untreated; 15 μg/ml CRP with or without 1 μM PPARδ agonists (L-165041). CRP increased PPARδ and interleukin-6 expression in cardiomyocytes and H9c2 cardiomyoblasts. NF-κB inducing kinase (NIK) and NF-κB pathway also activated by CRP stimulation. These changes could be inhibited by L-165041 through p38MAPK and c-JNK pathways. However, transfection with siRNA of CD32 CRP receptor did not decrease CRP signaling or reverse the effects of L-165041 in CRP-treated cardiomyocytes and H9c2. Pretreatment with L-165041 attenuated apoptosis induced by hypoxia with or without CRP in H9c2 cardiomyoblasts. CRP up-regulated PPARδ expression in cardiomyocytes and H9c2. L-165041 attenuated CRP-induced pro-inflammatory signaling through p38MAPK and c-JNK in H9c2 cardiomyoblasts. However, PPARδ activation attenuated CRP-induced NF-κB pathway may be independent of CD32. These results may provide new evidence of PPARδ beneficial effects for inflammatory cardiomyopathy.

Advanced glycation end products‐induced apoptosis attenuated by PPARδ activation and epigallocatechin gallate through NF‐κB pathway in human embryonic kidney cells and human mesangial cells

Diabetic nephropathy has attracted many researchers' attention. Because of the emerging evidence about the effects of advanced glycation end products (AGEs) and receptor of AGE (RAGE) on the progression of diabetic nephropathy, a number of different therapies to inhibit AGE or RAGE are under investigation. The purpose of the present study was to examine whether peroxisome proliferator-activated receptor delta (PPARdelta) agonist (L-165041) or epigallocatechin gallate (EGCG) alters AGE-induced pro-inflammatory gene expression and apoptosis in human embryonic kidney cells (HEK293) and human mesangial cells (HMCs). The HEK cells and HMC were separated into the following groups: 100 microg/mL AGE alone for 18 h; AGE treated with 1 microM L-165041 or 10 microM EGCG, and untreated cells. Inflammatory cytokines, nuclear factor-kappaB pathway, RAGE expression, superoxide dismutase and cell apoptosis were determined. AGE significantly increased tumour necrosis factor-alpha (TNF-alpha), a major pro-inflammatory cytokine. The mRNA and protein expression of RAGE were up-regulated. These effects were significantly attenuated by pre-treatment with L-165041 or EGCG. AGE-induced nuclear factor-kappaB pathway activation and both cells apoptosis were also inhibited by L-165041 or EGCG. Furthermore, both L-165041 and EGCG increased superoxide dismutase levels in AGE-treated HEK cells and HMC. This study demonstrated that PPARdelta agonist and EGCG decreased the AGE-induced kidney cell inflammation and apoptosis. This study provides important insights into the molecular mechanisms of EGCG and PPARdelta agonist in attenuation of kidney cell inflammation and may serve as a therapeutic modality to treat patients with diabetic nephropathy.

Postnatal PPARδ Activation and Myostatin Inhibition Exert Distinct yet Complimentary Effects on the Metabolic Profile of Obese Insulin-Resistant Mice

BackgroundInterventions for T2DM have in part aimed to mimic exercise. Here, we have compared the independent and combined effects of a PPARδ agonist and endurance training mimetic (GW501516) and a myostatin antibody and resistance training mimetic (PF-879) on metabolic and performance outcomes in obese insulin resistant mice.Methodology/Principal FindingsMale ob/ob mice were treated for 6 weeks with vehicle, GW501516, PF-879, or GW501516 in combination with PF-879. The effects of the interventions on body composition, glucose homeostasis, glucose tolerance, energy expenditure, exercise capacity and metabolic gene expression were compared at the end of study. GW501516 attenuated body weight and fat mass accumulation and increased the expression of genes of oxidative metabolism. In contrast, PF-879 increased body weight by driving muscle growth and altered the expression of genes involved in insulin signaling and glucose metabolism. Despite their differences, both interventions alone improved glucose homeostasis. Moreover, GW501516 more effectively improved serum lipids, and PF-879 uniquely increased energy expenditure, exercise capacity and adiponectin levels. When combined the robust effects of GW501516 and/or PF-879 on body weight, adiposity, muscle mass, glycemia, serum lipids, energy expenditure and exercise capacity were highly conserved.Conclusions/SignificanceThe data, for the first time, demonstrate postnatal inhibition of myostatin not only promotes gains in muscle mass similar to resistance training,but improves metabolic homeostasis. In several instances, these effects were either distinct from or complimentary to those of GW501516. The data further suggest that strategies to increase muscle mass, and not necessarily oxidative capacity, may effectively counter insulin resistance and T2DM.

Activation of PPARδ promotes mitochondrial energy metabolism and decreases basal insulin secretion in palmitate-treated β-cells

The peroxisome proliferator-activated receptor δ (PPARδ) regulates the expression of genes involved in cellular lipid and cell energy metabolism in many metabolically active tissues, such as liver, muscle, and fat, and plays a role in the cellular response to stress and environmental stimuli. The particular role of PPARδ in insulin-secreting β-cells, however, is not well understood; we recently identified the cell-specific role of PPARδ on mitochondrial energy metabolism and insulin secretion in lipotoxic β-cells. After treatment of HIT-T15 cells, a syrian hamster pancreatic β-cell line, with high concentrations of palmitate and/or the specific PPARδ agonist GW501516, we detected the gene expression changes for transcripts, such as peroxisome proliferator-activated receptor gamma co-activator 1 (PGC-1α), nuclear respiratory factor 1 (NRF-1), mitochondrial transcription factor A (mtTFA), the protein levels of the mitochondria uncoupling protein 2 (UCP2), mitochondrial morphology, the insulin secretion capacity and ATP/ADP ratio. Our results show that GW501516 treatment promoted generation of mitochondrial ATP, as well as expression levels of PGC-1α, NRF-1 and mtTFA, decreased basal insulin secretion, but had no effect on glucose-stimulated insulin secretion (GSIS), increased amounts of UCP2 and changed ATP-to-ADP ratio, improved mitochondrial morphology in palmitate-treated β-cells. GW501516-induced activation of PPARδ enhanced mitochondrial energy metabolism, but also promoted a concomitant mitochondrial uncoupling and resulted in decreased basal insulin secretion and restricted GSIS; this observation indicated the possible action of a protective mechanism responding to the alleviation of excessive lipid load and basal insulin secretion in lipotoxic β-cells.

PPARδ promotes wound healing by up‐regulating TGF‐β1‐dependent or ‐independent expression of extracellular matrix proteins

Although the peroxisome proliferator-activated receptor (PPAR) δ has been implicated in the wound healing process, its exact role and mechanism of action have not been fully elucidated. Our previous findings showed that PPARδ induces the expression of the transforming growth factor (TGF)-β1, which has been implicated in the deposit of extracellular matrix proteins. Here, we demonstrate that administration of GW501516, a specific PPARδ ligand, significantly promoted wound closure in the experimental mouse and had a profound effect on the expression of collagen types I and III, alpha-smooth muscle actin, pSmad3 and TGF-β1, which play a pivotal role in wound healing processes. Activation of PPARδ increased migration of human epidermal keratinocytes and dermal fibroblasts in in vitro scrape-wounding assays. Addition of a specific ALK5 receptor inhibitor SB431542 significantly suppressed GW501516-induced migration of human keratinocytes and fibroblasts. In these cells, activated PPARδ also induced the expression of collagen types I and III and fibronectin in a TGF-β1-dependent or -independent manner. The effect of PPARδ on the expression of type III collagen was dually regulated by the direct binding of PPARδ and Smad3 to a direct repeat-1 site and a Smad-binding element, respectively, of the type III gene promoter. Taken together, these results demonstrated that PPARδ plays an important role in skin wound healing in vivo and that it functions by accelerating extracellular matrix-mediated cellular interactions in a process mediated by the TGF-β1/Smad3 signaling-dependent or - independent pathway.