Effect Of Peroxisome Proliferator-activated Receptor Gamma Research Articles

A selective peroxisome proliferator-activated receptor-γ agonist benefited propionic acid induced autism-like behavioral phenotypes in rats by attenuation of neuroinflammation and oxidative stress

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder in children. It is diagnosed by two main behavioral phenotypes i.e. social-communication impairments and repetitive behavior. ASD is complex disorder with unsolved etiology due to multiple genes involvement, epigenetic mechanism and environmental factors. The clinical and preclinical studies have been indicating the association of propionic acid with autism spectrum disorder. Numerous studies suggest the potential therapeutic effects of peroxisome proliferator-activated receptor-gamma (PPAR-γ) in different brain disorders. This research evaluates the utility of selective agonist of PPAR-γ, pioglitazone in postnatal propionic acid induced ASD related symptomatology in male Wistar rats. PPA (250 mg/kg, p.o.) was administered to male offspring for three consecutive days from postnatal 21st day to 23rd day. PPA induced social impairment, repetitive behavior, hyperlocomotion, anxiety and low exploratory activity in rats. Also, postnatal propionic acid-treated rats showed higher levels of oxidative stress (increased in thiobarbituric acid reactive species and decreased in reduced glutathione) as well as inflammation (increased in interleukin-6, tumor necrosis factor-alpha and decreased in interleukin-10) in the cerebellum, brainstem and prefrontal cortex. The rats were treated daily with pioglitazone (10 mg/kg and 20 mg/kg, p.o.) from postnatal 24th day to end of the study. Treatment with pioglitazone, significantly attenuated the postnatal propionic acid-induced social impairment, repetitive behavior, hyperactivity, anxiety and low exploratory activity. Furthermore, pioglitazone also reduced the postnatal propionic acid-induced oxidative stress and neuroinflammation in aforementioned brain regions. Hence, pioglitazone improved the propionic acid-induced neurobehavioral and biochemical impairments in rats.

Beneficial effects of pioglitazone, a selective peroxisome proliferator-activated receptor-γ agonist in prenatal valproic acid-induced behavioral and biochemical autistic like features in Wistar rats

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder in children. It is diagnosis by two main behavioral phenotypes i.e. social-communication impairments and repetitive behavior. ASD is complex disorder with unsolved etiology due to multiple genes involvement, epigenetic mechanism and environmental factors. Valproic acid (VPA), a teratogen is known to induce characteristic features related to ASD in rodents. Numerous studies suggest the potential therapeutic effects of peroxisome proliferator-activated receptor-gamma (PPAR-γ) in different brain disorders. This research evaluates the utility of selective agonist of PPAR-γ, pioglitazone in prenatal VPA induced experimental ASD symptomatology in Wistar rats. The prenatal administration of VPA has induced social impairment, repetitive behavior, hyperlocomotion, anxiety and low exploratory activity in rats. Also, prenatal VPA-treated rats have shown higher levels of oxidative stress (increased in thiobarbituric acid reactive species, and decreased in reduced glutathione level) and inflammation (increased in interleukin-6, tumor necrosis factor-alpha and decreased in interleukin-10) in the cerebellum, brainstem and prefrontal cortex. Treatment with pioglitazone significantly attenuated the prenatal VPA-induced social impairment, repetitive behavior, hyperactivity, anxiety and low exploratory activity. Furthermore, pioglitazone also reduced the prenatal VPA-induced oxidative stress and neuroinflammation in aforementioned brain regions. Hence, it may be concluded that pioglitazone may provide neurobehavioral and biochemical benefits in prenatal VPA-induced autistic phenotypes in rats.

Pulmonary Hypertension and Obesity: Focus on Adiponectin.

Pulmonary hypertension is an umbrella term including many different disorders causing an increase of the mean pulmonary arterial pressure (mPAP) ≥ 25 mmHg. Recent data revealed a strong association between obesity and pulmonary hypertension. Adiponectin is a protein synthetized by the adipose tissue with pleiotropic effects on inflammation and cell proliferation, with a potential protective role on the pulmonary vasculature. Both in vivo and in vitro studies documented that adiponectin is an endogenous modulator of NO production and interferes with AMP-activated protein kinase (AMPK) activation, mammalian target of rapamycin (mTOR), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κβ) signaling preventing endothelial dysfunction and proliferation. Furthermore, adiponectin ameliorates insulin resistance by mediating the biological effects of peroxisome proliferator-activated receptor-gamma (PPARγ). Therefore, adiponectin modulation emerged as a theoretical target for the treatment of pulmonary hypertension, currently under investigation. Recently, consistent data showed that hypoglycemic agents targeting PPARγ as well as renin–angiotensin system inhibitors and mineralocorticoid receptor blockers may influence pulmonary hemodynamics in different models of pulmonary hypertension.

Abstract 332: Retinol-binding Protein 7 (RBP7) Regulates Endothelial Function, Independent of Metabolic Responses in High-fat Diet Fed Mice

Peroxisome proliferator-activated receptor gamma (PPARG), a ligand-activated transcription factor, plays a protective role in the endothelium through mechanisms that remain unclear. RBP7 is an intracellular retinoid binding protein belonging to the family of fatty acid-binding proteins (FABP) and is a PPARG target. RBP7 expression was increased 2.6-fold by rosiglitazone (RZ), a PPARG agonist in mouse lung endothelial cells, which was blocked by GW9662, a PPARG antagonist. We hypothesized that the protective effects of PPARG on the endothelium are mediated by RBP7. Studies were performed in: 20-week HFD-fed RBP7-deficient (KO) and wild type (WT) and age-matched chow-fed KO and WT mice. HFD increased fasting glucose in both WT and KO mice compared to chow-fed groups, and caused similar hepatic steatosis. HFD-fed mice were more glucose-intolerant and insulin-resistant compared with chow-fed mice, but there were no differences comparing KO with WT mice. Weight gain in response to HFD was also similar in KO and WT mice. Thus KO and WT mice exhibited similar HFD-induced metabolic dysfunction. Endothelium-dependent relaxation to acetylcholine (Ach) was normal in chow-fed KO mice, but was impaired in carotid artery of HFD-fed KO mice (49±6% KO vs 70±4% WT, p<0.05, 30μM Ach). Endothelial-independent relaxation was similar in all groups. Superoxide production in carotid artery (DHE-fluorescence) was elevated 1.5-fold in HFD-fed KO mice compared with the other 3 groups. Normal relaxation to Ach was restored by anti-oxidant treatment, suggesting HFD causes oxidative stress in the absence of RBP7. Systolic blood pressure was similar in HFD-fed KO and WT mice (110±4 mmHg in KO vs 105±0 mmHg in WT). Because other members of the FABP family facilitate steroid hormone receptor function, we hypothesized that RBP7 may facilitate PPARG function. To initially test this, we examined the cellular localization of an RBP7-GFP fusion protein. In vehicle treated COS7 cells, RBP7 was distributed both in cytoplasm and nucleus. RZ treatment resulted in a robust shift of RBP7 into the nucleus. In conclusion, RBP7 protects the endothelium from HFD-induced oxidative and vascular dysfunction, independent of changes to systemic metabolism.

Regulation of cigarette smoke‐induced toll‐like receptor 4 expression by peroxisome proliferator‐activated receptor‐gamma agonists in bronchial epithelial cells

This study was designed to determine the effects of peroxisome proliferator-activated receptor-gamma (PPARγ) on airway inflammatory response to cigarette smoke (CS) exposure. For the in vivo experiments, 50 male Wistar rats were randomly assigned to one of four groups and were exposed to CS and pretreatment with a PPARγ agonist, rosiglitazone or a vehicle (saline). PPARγ antagonist bisphenol A diglycidyl ether (BADGE) or saline was administered before rosiglitazone treatment. Leukotriene B4 (LTB4) and interleukin-8 (IL-8) were measured by enzyme-linked immunosorbent assay. PPARγ and toll-like receptor 4 (TLR4) expression levels were assessed by immunohistochemistry and real-time polymerase chain reaction. For the in vitro experiments, human bronchial epithelial cells were stimulated with CS or phosphate buffer saline, pretreated with PPARγ agonist rosiglitazone or 15-deoxy-(Δ12,14)-PG J2 before CS exposure. BADGE was administered prior to the agonist treatment. PPARγ, TLR4 and inhibitor of κB (IκBα) expression levels were assessed by Western bot. CS exposure decreased PPARγ expression, as well as increased IL-8, LTB4 and TLR4 expression levels in bronchial epithelial cells in vivo and in vitro. Moreover, PPARγ ligands counteracted CS-induced airway inflammation by reducing IL-8 and LTB4 expression levels that are associated with TLR4 and nuclear factor-kappa B (NF-κB). CS exposure increased the pro-inflammatory activity of bronchial epithelial cells by affecting PPARγ expression. Moreover, PPARγ may play a significant role as a modulator of the TLR4-dependent inflammatory pathway through NF-κB in bronchial epithelial cells.

Abstract 21: Retinol-binding Protein 7 (RBP7), a Peroxisome Proliferator-Activated Receptor Gamma (PPARG) Target Gene, is a Novel Regulator of Endothelial Function

PPARG, a ligand-activated transcription factor, in the endothelium regulates vascular function and blood pressure, through mechanisms that remain poorly defined. Endothelial-specific expression of dominant negative (DN) PPARG (E-V290M) caused endothelial dysfunction when combined with a high fat diet (HFD). RBP7 is an intracellular retinoid binding protein belonging to the family of fatty acid-binding proteins and a PPARG target gene. RBP7 expression in aorta is induced by rosiglitazone and repressed by DN PPARG, and its level of expression is highly correlated with PPARG in other tissues. RBP7 is also expressed in endothelium. We hypothesize that RBP7 may mediate some vascular protective effects of PPARG during HFD. We examined vascular responses in basilar artery (BA, pressurized myograph) and carotid artery (CA, wire myograph) of RBP7-deficient (KO), heterozygous (HZ), and wild type (WT) mice fed normal chow diet (ND) or HFD for 8 or 20 wks. Weight gain was similar in all three HFD-fed groups and was higher than ND-fed mice. There was no difference in the endothelium-dependent, acetylcholine (ACh)-induced relaxation in either BA or CA of any group under ND. Following 8 wks HFD, BA from KO mice exhibited impaired relaxation to ACh compared to control mice (at 100μM: 33±7% KO vs 73±7% HZ vs 83±10% WT, p<0.05). A normal response was observed to the nitric oxide donor, nitroprusside (SNP). An impaired ACh-, but not SNP- or papaverine-induced relaxation was observed in CA of KO mice after 20 wks of HFD (ACh 30μM: 49±6% KO vs 61±3% HZ vs 70±4% WT, p<0.05). No differences were found in phenylephrine- and endothelin-1-induced contractions in CA in any group. Pre-incubation of BA for 30 minutes with the superoxide scavengers tempol (1mM) or PEG-superoxide dismutase (PEG-SOD, 100 U/ml) completely restored ACh-induced relaxation to normal (ACh at 100μM: 79±7% Tempol-KO; 75±12% PEG-SOD-KO; 81±11% WT). This phenotype was very similar to that observed in HFD fed E-V290M mice. We conclude that loss of RBP7 causes endothelial dysfunction in response to a HFD through a mechanism involving oxidative stress. These findings provide the first evidence that RBP7 plays a protective role in the endothelium, which might be related to the endothelial protective effects of PPARG.

Abstract 74: Endothelial PPARγ Protects Against Vascular Thrombosis by Downregulating P-Selectin-Mediated Leukocyte-Endothelial Interactions

Background and Hypothesis: Tissue-specific effects of peroxisome proliferator-activated receptor-gamma (PPARγ) on vascular thrombosis are not well understood. Using a novel murine model of selective interference with endothelial PPARγ, we tested the hypothesis that endothelial PPARγ protects against vascular thrombosis. Methods: Transgenic mice expressing a dominant negative PPARγ mutant (E-V290M) selectively in endothelium were compared with non-transgenic (non-Tg) littermates. Susceptibility to occlusive thrombosis of the carotid artery was assessed following chemical (7% FeCl3) or photochemical (rose bengal and green laser) injury. Leukocyte rolling on mesenteric venules was measured by intravital microscopy. P-selectin mRNA levels were assayed by real-time PCR and P-selectin protein levels were measured by ELISA and flow cytometry. To assess the role of P-selectin and leukocytes in thrombosis, P-selectin blocking antibodies or leukocyte-depleting antibodies were infused before carotid artery injury. Results: The time to occlusion of the carotid artery was significantly shortened in E-V290M mice compared with non-Tg mice after either chemical (5.1±0.2 vs. 10.1±3.3 vs. minutes; P=0.01) or photochemical injury (48±9 vs. 74±9 minutes; P=0.04). Both plasma P-selectin levels and P-selection mRNA levels in the carotid artery were significantly higher in E-V290M mice than in non-Tg mice (P<0.05), but no differences in platelet surface P-selectin were observed. Increased functional endothelial P-selectin activity was demonstrated by enhanced leukocyte rolling on mesenteric venules in E-V290M mice compared with non-Tg mice (53±8 vs. 25±7 per minute; P=0.025). The shortened occlusion times in E-V290M mice were reversed by P-selectin blocking antibodies or leukocyte-depleting antibodies (P=0.04, and P=0.02 respectively). Gene set enrichment analysis of a gene expression microarray demonstrated significant upregulation of NF-kB target genes, including P-selectin, in endothelial cells from E-V290M mice (P<0.001). Conclusions: We conclude that endothelial PPARγ protects from thrombosis through a mechanism that involves downregulation of NF-kB-mediated P-selectin expression and leukocyte-endothelial interactions.

PPAR-γ signaling and IL-5 inhibition together prevent chronic rejection of MHC Class II–mismatched cardiac grafts

Chronic rejection can prevent long-term survival of organ transplants. Although the beneficial effects of peroxisome proliferator-activated receptor-gamma (PPAR-γ) in reducing graft rejection have been reported, the details of the underlying mechanisms remain unclear, especially in the context of modulating cellular infiltration and preventing vasculopathy and interstitial fibrosis. The therapeutic effects of the PPAR-γ agonist, rosiglitazone, combined with anti-interleukin-5 are explored in a mouse model of MHC Class II-histoincompatible cardiac transplantation. Rosiglitazone treatment alone marginally increased long-term survival and reduced CD8 T-cell infiltration and vasculopathy in the grafts. However, there was no reduction in collagen deposition and interleukin (IL)-4, IL-5 and eosinophil infiltration were increased. Anti-IL-5 antibody treatment alone reduced eosinophil infiltration and collagen deposition, but had no effect on CD8 T-cell infiltration or vasculopathy. Combined treatment with anti-IL-5 antibody and rosiglitazone prevented graft rejection. Furthermore, rosiglitazone treatment increased adiponectin receptor II expression in grafts and on dendritic cells and T cells in vitro. Graft survival correlated with increased expression in grafts of the inhibitory molecule PD-L1. The findings obtained increase the knowledge on the mode of action of rosiglitazone in promoting the survival of MHC Class II-mismatched cardiac transplants in which the CD8 T cells and eosinophils play key roles. PPAR-γ signaling combined with IL-5 blockade prevents graft rejection.

PPARγ agonist pioglitazone inhibits microglia inflammation by blocking p38 mitogen-activated protein kinase signaling pathways

The aim of this paper was to investigate the inhibitory effect of peroxisome proliferator-activated receptor-gamma (PPARγ) agonist pioglitazone on microglia inflammation induced by lipopolysaccharide (LPS). Highly aggressively proliferating immortalized cells were used from a rat microglial cell line. Expression of PPARγ, inducible NO synthase (iNOS), the p42/44 extracellular signal-regulated kinase (ERK) MAPKs, c-Jun NH2-terminal kinases (JNKs) and p38 MAPK were determined by Western blot analysis. The protein levels of tumor necrosis factor α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β) were determined by enzyme-linked immunosorbent assay. The production of nitric oxide (NO) was determined by a Nitric Oxide Assay Kit. The subcellular localization of PPARγ was studied by immunofluorescence microscopy analysis and nuclear-cytosolic fractionation technology, respectively. The transcriptional activity of PPARγ was detected by PPRE-Luciferase transcription assay. Pioglitazone effectively inhibited NO, iNOS, TNF-α, IL-6, IL-1β production in LPS-stimulated microglial cells. Additionally, pioglitazone suppressed PPARγ loss; enhanced transcriptional activity of PPARγ; and inhibited nucleus-export of PPARγ in microglia induced by LPS. And p38 MAPK inhibitor SB203580 had the similarity effects with pioglitazone. Signal transduction studies indicated that pioglitazone blocked the phosphorylation of p38 MAPK challenged by LPS. The results show that pioglitazone can inhibit LPS-stimulated microglia inflammation by blocking p38 MAPK signaling pathway.

Activation of peroxisome proliferator-activated receptor-γ induces apoptosis on acute promyelocytic leukemia cells via downregulation of XIAP

In the present study we investigated the in vitro apoptosis inducing effects of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) ligand ciglitazone (CGZ) on acute promyelocytic leukemia (APL) NB4 cells and its mechanisms of action. The results revealed that CGZ (10-50 micromol/l) inhibited the growth of leukemia NB4 cells and caused apoptosis in a time- and dose-dependent manner. Apoptosis was observed clearly by flow cytometry (FCM) and DNA fragmentation analysis. After treatment by CGZ for 48 h, the percentage of disruption of mitochondrial membrane potential (Deltapsim) was increased in a dose-dependent manner. Western blotting demonstrated the cleavage of caspase-3 zymogen protein and a time-dependent cleavage of poly (ADP-ribose) polymerase (PARP). The results also demonstrated that PPAR-gamma expression was increased concomitantly when apoptosis occurred, and that CGZ-induced apoptosis was inhibited by the PPAR-gamma antagonist GW9662, suggesting a PPAR-gamma dependent signaling pathway in CZG-induced cell death. Moreover, CGZ treatment remarkably downregulated the expression of the X-linked inhibitor of apoptosis protein (XIAP), which was inhibited by GW9662. Of note, a small-molecule XIAP antagonist (1396-12) mimicked the effect of CGZ-induced apoptosis via activation of caspase-3, 7 and 9. The apoptosis-inducing effects by CGZ on fresh APL cells were also found to be remarkable by using FCM and Wright's staining observation. Taken together, our results suggest that downregulation of XIAP and activation of capase-3 play an important role in mediating the PPAR-gamma-dependent cell death induced by CGZ in APL cells. These data provide a novel insight into potential therapeutic strategies for treatment of leukemia.

Proteasome inhibition overcomes the resistance of renal cell carcinoma cells against the PPARgamma ligand troglitazone.

In order to analyze the effects of peroxisome proliferator-activated receptor-gamma (PPARgamma) activation on renal cell carcinomas we utilized several cell lines that were treated with the high affinity PPARgamma agonist, troglitazone. Incubation of RCC cells with troglitazone resulted in reduced secretion of growth factors that was due to the inhibition of MAP kinase signaling and reduced nuclear localized expression of relB and HIF1alpha. Interestingly, the cell lines used showed a different sensitivity towards apoptosis induction that did not correlate with the inhibition of growth factors or expression of pro- and antiapoptotic molecules. To overcome this resistance the cells were treated with a combination of troglitazone and the proteasome inhibitor, bortezomib. The combination of both compounds induced apoptosis even in cells resistant to both agents alone, due to increased induction of ER-stress and caspase-3 mediated cell death.

PPARγ ligands, rosiglitazone and pioglitazone, inhibit bFGF- and VEGF-mediated angiogenesis

To study the effect of peroxisome proliferator-activated receptor-gamma (PPAR gamma) agonists, pioglitazone and rosiglitazone, on vascular endothelial growth factor (VEGF)- and basic fibroblast growth factor (bFGF)-induced angiogenesis and on endothelial cell migration. Chick chorioallantoic membrane (CAM) model was used to evaluate the efficacy of pioglitazone and rosiglitazone on VEGF- and bFGF-induced angiogenesis. In addition, the effect of pioglitazone and rosiglitazone on endothelial cell migration was evaluated using 8 mm pore filter to a feeder layer containing vitronectin as chemoattractant. Pioglitazone and rosiglitazone inhibited the pro-angiogenic effects of bFGF and VEGF in the CAM model significantly (P < 0.001) to the same extent. Endothelial cell migration was also inhibited by both pioglitazone and rosiglitazone (P < 0.001). These results suggest that PPAR gamma ligands, pioglitazone and rosiglitazone, in addition to their important regulatory role in adipogenesis and inflammation, possess anti-angiogenic properties. Thus, PPAR gamma ligands may be useful in the treatment of diabetic retinopathy, macular degeneration, and other ocular disorders and may lower the risk to develop cancer in diabetic patients.

(117) Peroxisome proliferator-activated receptor-gamma activation reverses existing hypersensitivity in diabetic neuropathic rats: Possible mechanisms

Various in vivo and in vitro studies and recent reports from our lab have shown the anti-inflammatory and antinociceptive effect of peroxisome proliferator-activated receptor-gamma (PPAR-γ) in a number of experimental acute pain and inflammation models. However, the role of PPAR-γ activation on diabetic neuropathic pain is not known. Further, its effect on oxidative stress and proinflammatory cytokines related to the maintenance of hypersensitivity is not yet studied. Thus, the present study was designed to investigate the effect of pioglitazone (PIO), a PPAR-γ agonist, on hyperalgesia and allodynia in streptozotocin-induced diabetic rats.