PPARγ-dependent Mechanism Research Articles

Relaxin causes selective outward remodeling of brain parenchymal arteriolesviaactivation of peroxisome proliferator‐activated receptor‐γ

Brain parenchymal arterioles (PAs), but not pial arteries, undergo hypotrophic outward remodeling during pregnancy that involves peroxisome proliferator-activated receptor-γ (PPARγ) activation. Relaxin, a peptide hormone produced during pregnancy, is involved in systemic and renal artery remodeling and activates PPARγ in vitro. Thus, we hypothesized that relaxin is involved in the selective outward remodeling of PAs through a PPARγ-dependent mechanism. Nonpregnant rats were treated with relaxin (4 μg/h, osmotic minipump), relaxin plus PPARγ inhibitor GW9662 (10 mg/kg/d), or vehicle for 10 d. Vascular function and structure were compared in isolated and pressurized middle cerebral arteries (MCAs) and PAs taken from the same animals. Relaxin treatment increased serum relaxin to the level of pregnancy (54 ng/ml) and increased passive wall thickness (hypertrophy; 70 ± 5 vs. 54 ± 4 μm in vehicle; P<0.05) and inner diameter (outward remodeling; 10.6 ± 0.5 vs. 8.0 ± 0.6 μm in vehicle; P<0.05) in PAs, but not in MCAs. This hypertrophic outward remodeling was prevented by GW9662 that had diameters (57 ± 3 μm) and wall thickness (8.6 ± 1.0 μm) similar to vehicle. GW9662 also prevented relaxin-induced changes in PPARγ target gene expression. These results suggest that relaxin produced during pregnancy may be partly responsible for selective remodeling of PAs during pregnancy through a mechanism involving PPARγ

The citrus flavonoid hesperidin induces p53 and inhibits NF-κB activation in order to trigger apoptosis in NALM-6 cells: involvement of PPARγ-dependent mechanism

Hesperidin, a flavanone present in citrus fruits, has been identified as a potent anticancer agent because of its proapoptotic and antiproliferative characteristics in some tumor cells. However, the precise mechanisms of action are not entirely understood. The main purpose of this study is to investigate the involvement of peroxisome proliferator-activated receptor-gamma (PPARγ) in hesperidin's anticancer actions in human pre-B NALM-6 cells, which expresses wild-type p53. The effects of hesperidin on cell-cycle distribution, proliferation, and caspase-mediated apoptosis were examined in NALM-6 cells in the presence or absence of GW9662. The expression of peroxisome proliferator-activated receptor-gamma (PPARγ), p53, phospho-IκB, Bcl-2, Bax, and XIAP proteins were focused on using the immunoblotting assay. The transcriptional activities of PPARγ and nuclear factor-kappaB (NF-κB) were analyzed by the transcription factor assay kits. The expression of PPARγ and p53 was analyzed using the RT-PCR method. Hesperidin induced the expression and transcriptional activity of PPARγ and promoted p53 accumulation and downregulated constitutive NF-κB activity in a PPARγ-dependent and PPARγ-independent manner. The growth-inhibitory effect of hesperidin was partially reduced when the cells preincubated with PPARγ antagonist prior to the exposure to hesperidin. The findings of this study clearly demonstrate that hesperidin-mediated proapoptotic and antiproliferative actions are regulated via both PPARγ-dependent and PPARγ-independent pathways in NALM-6 cells. These data provide the first evidence that hesperidin could be developed as an agent against hematopoietic malignancies.

Corrigendum

CorrigendumCorrigendumPublished Online:01 Feb 2011https://doi.org/10.1152/ajpheart.zh4-9722-corr.2011Original articleMoreSectionsPDF (49 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Volume 299, September 2010Volume 68, September 2010Pages H690–H698: Amin RH, Mathews ST, Alli A, Leff T. Endogenously produced adiponectin protects cardiomyocytes from hypertrophy by a PPAR-dependent autocrine mechanism. Am J Physiol Heart Circ Physiol 299: , 2010. First published July 9, 2010; doi:10.1152/ajpheart.01032.2009. (http://ajpheart.physiology.org/cgi/content/full/299/3/H690).—On p. H692, Fig. 1E was misrepresented; it appeared as a duplicate of Fig. 1C. The correct Fig. 1E is presented below.Download figureDownload PowerPointThis article has no references to display. Download PDF Previous Back to Top FiguresReferencesRelatedInformationRelated ArticlesEndogenously produced adiponectin protects cardiomyocytes from hypertrophy by a PPARγ-dependent autocrine mechanism 01 Sep 2010American Journal of Physiology-Heart and Circulatory Physiology More from this issue > Volume 300Issue 2February 2011Pages H714-H714 Copyright & PermissionsCopyright © 2011 the American Physiological Societyhttps://doi.org/10.1152/ajpheart.zh4-9722-corr.2011History Published online 1 February 2011 Published in print 1 February 2011 Metrics

Abscisic Acid Regulates Inflammation via Ligand-binding Domain-independent Activation of Peroxisome Proliferator-activated Receptor γ

Abscisic acid (ABA) has shown efficacy in the treatment of diabetes and inflammation; however, its molecular targets and the mechanisms of action underlying its immunomodulatory effects remain unclear. This study investigates the role of peroxisome proliferator-activated receptor γ (PPAR γ) and lanthionine synthetase C-like 2 (LANCL2) as molecular targets for ABA. We demonstrate that ABA increases PPAR γ reporter activity in RAW 264.7 macrophages and increases ppar γ expression in vivo, although it does not bind to the ligand-binding domain of PPAR γ. LANCL2 knockdown studies provide evidence that ABA-mediated activation of macrophage PPAR γ is dependent on lancl2 expression. Consistent with the association of LANCL2 with G proteins, we provide evidence that ABA increases cAMP accumulation in immune cells. ABA suppresses LPS-induced prostaglandin E(2) and MCP-1 production via a PPAR γ-dependent mechanism possibly involving activation of PPAR γ and suppression of NF-κB and nuclear factor of activated T cells. LPS challenge studies in PPAR γ-expressing and immune cell-specific PPAR γ null mice demonstrate that ABA down-regulates toll-like receptor 4 expression in macrophages and T cells in vivo through a PPAR γ-dependent mechanism. Global transcriptomic profiling and confirmatory quantitative RT-PCR suggest novel candidate targets and demonstrate that ABA treatment mitigates the effect of LPS on the expression of genes involved in inflammation, metabolism, and cell signaling, in part, through PPAR γ. In conclusion, ABA decreases LPS-mediated inflammation and regulates innate immune responses through a bifurcating pathway involving LANCL2 and an alternative, ligand-binding domain-independent mechanism of PPAR γ activation.

T cell PPARγ is required for the anti-inflammatory efficacy of abscisic acid against experimental IBD

The phytohormone abscisic acid (ABA) has been shown to be effective in ameliorating chronic and acute inflammation. The objective of this study was to investigate whether ABA's anti-inflammatory efficacy in the gut is dependent on peroxisome proliferator-activated receptor γ (PPARγ) in T cells. PPARγ-expressing and T cell-specific PPARγ null mice were fed diets with or without ABA (100 mg/kg) for 35 days prior to challenge with 2.5% dextran sodium sulfate. The severity of clinical disease was assessed daily, and mice were euthanized on Day 7 of the dextran sodium sulfate challenge. Colonic inflammation was assessed through macroscopic and histopathological examination of inflammatory lesions and real-time quantitative RT-PCR-based quantification of inflammatory genes. Flow cytometry was used to phenotypically characterize leukocyte populations in the blood and mesenteric lymph nodes. Colonic sections were stained immunohistochemically to determine the effect of ABA on colonic regulatory T (T reg) cells. ABA's beneficial effects on disease activity were completely abrogated in T cell-specific PPARγ null mice. Additionally, ABA improved colon histopathology, reduced blood F4/80 +CD11b + monocytes, increased the percentage of CD4 + T cells expressing the inhibitory molecule cytotoxic T lymphocyte antigen 4 in blood and enhanced the number of T reg cells in the mesenteric lymph nodes and colons of PPARγ-expressing but not T cell-specific PPARγ null mice. We conclude that dietary ABA ameliorates experimental inflammatory bowel disease by enhancing T reg cell accumulation in the colonic lamina propria through a PPARγ-dependent mechanism.

Docosahexaenoic acid increases cellular adiponectin mRNA and secreted adiponectin protein, as well as PPARγ mRNA, in 3T3-L1 adipocytes

Adiponectin, a protein secreted from adipose tissue, has been shown to have anti-diabetic and anti-inflammatory effects, but its regulation is not completely understood. Long-chain n-3 fatty acids eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA) may be involved in adiponectin regulation as they are potential ligands for peroxisome proliferator-activated receptor-γ (PPARγ), a key transcription factor for the adiponectin gene. To examine this, 3T3-L1 adipocytes were incubated with 125µmol·L-1 EPA, DHA, palmitic, or oleic acids complexed to albumin, or with albumin alone (control) for 24h. Adipocytes were also incubated for 24h with EPA and DHA plus bisphenol-A-diglycidyl ether (BADGE), a PPARγ antagonist. Both EPA and DHA increased (p< 0.05) secreted adiponectin concentration compared with the control (44% and 102%, respectively), but did not affect cellular adiponectin protein content. Incubation with BADGE and DHA inhibited increases in secreted adiponectin protein, suggesting that DHA may act through a PPARγ-dependent mechanism. However, BADGE had no effect on EPA-induced increases in secreted adiponectin protein. Only DHA enhanced (p< 0.05) PPARγ and adiponectin mRNA expression compared wtih the control. Our results demonstrate that DHA increases cellular adiponectin mRNA and secreted adiponectin protein in 3T3-L1 adipocytes, possibly by a mechanism involving PPARγ. Moreover, DHA increased adiponectin concentration to a greater extent (40% more, p< 0.05) compared with EPA, emphasizing the need to consider the independent actions of EPA and DHA in adipocytes.

Endogenously produced adiponectin protects cardiomyocytes from hypertrophy by a PPARγ-dependent autocrine mechanism

In experimental animal and cell culture models, activation of peroxisome proliferator-activated receptor (PPAR) gamma in heart has been shown to have beneficial effects on cardiac function and cardiomyocyte physiology. The goal of this study was to identify the signaling pathway by which PPARgamma activation protects cardiomyocytes from the deleterious effects of hypertrophic stimuli. In primary cardiomyocyte cultures, we found that genetic or pharmacological activation of PPARgamma protected cells from cardiac hypertrophy induced by alpha-adrenergic stimulation. Examination of gene expression in these cells revealed a surprising increase in the expression of adiponectin in cardiomyocytes and secretion of the high-molecular-weight form of the hormone into media. Using RNAi to block PPARgamma-induced adiponectin production or adiponectin receptor gene expression, we found that the PPARgamma-mediated anti-hypertrophic effect required cardiomyocyte-produced adiponectin, as well as an intact adiponectin signaling pathway. Furthermore, mice expressing constitutive-active PPARgamma and cardiomyocyte specific adiponectin expression were protected from high-fat diet-induced cardiac hypertrophy and remodeling. These findings demonstrate that functional adiponectin hormone can be produced from the heart and raise the possibility that beneficial effects of PPARgamma activation in heart could be due in part to local production of adiponectin that acts on cardiomyocytes in an autocrine manner.

Synergistic effects of telmisartan and simvastatin on endothelial progenitor cells

Circulating endothelial progenitor cells (EPC) contribute to endothelial replenishment. Telmisartan is an angiotensin-receptor blocker with PPARγ-agonistic properties. PPARγ-agonists and HMG-CoA reductase inhibitors have been shown to enhance EPC number and function. We focused on the effects of telmisartan alone or in combination with simvastatin on EPC. EPC were isolated from healthy human volunteers, cultured and stimulated with telmisartan, simvastatin, or the combination of telmisartan and simvastatin. Telmisartan significantly increased the number of acLDL/lectin double-positive early EPC, the number of colony forming units (EC-CFU) as well as EPC migratory capacity, inhibited TNFα-induced EPC apoptosis and reduced glucose-induced oxidative stress. The telmisartan effect was dose-dependent and could be inhibited by GW9662, indicating a PPARγ-dependent mechanism. The combination of telmisartan and simvastatin led to a significant additive increase in EPC count and function. In wild-type mice, systemic treatment with either telmisartan or simvastatin elevated the number of sca-1/flk-1-positive EPC in bone marrow and peripheral blood, spleen-derived acLDL/lectin double-positive EPC, EPC migration and EC-CFU. Consistent with the in vitro findings, the combination of telmisartan and simvastatin resulted in a further enhancement of EPC counts. Re-endothelialization after carotid injury was significantly enhanced by telmisartan, simvastatin and the combination. Telmisartan increases EPC number and function mediated by a PPARγ-dependent mechanism. This effect is further enhanced by combination with simvastatin, suggesting a synergistic activation of potentially diverse intracellular pathways.

Losartan inhibits LPS-induced inflammatory signaling through a PPARγ-dependent mechanism in human THP-1 macrophages

Macrophages have critical roles in the pathogenesis of atherosclerosis by activating the innate immune system and producing inflammatory cytokines. Accumulating evidence indicates that angiotensin type 1 receptor (AT1R) blockers exert anti-inflammatory effects in inflammatory diseases including atherosclerosis. In this study, we investigated the effect of losartan, an AT1R blocker, on the proinflammatory gene expression induced by bacterial lipopolysaccharide (LPS) in a well-defined in vitro human THP-1 macrophage system. We found that losartan significantly attenuated the LPS-induced expression of proinflammatory genes TNF-alpha, IL-8 and COX-2. However, exogenous angiotensin II (AngII) had no effect on LPS-induced inflammatory signaling despite the expression of AT1R. In addition, losartan did not block LPS-induced IkappaB phosphorylation, which is downstream of Toll-like receptor activation. Peroxisome proliferator-activated receptor-gamma (PPARgamma) antagonists, GW9662 and T0070907, reversed the inhibitory effects of losartan on LPS-induced TNF-alpha and IL-8 expression in THP-1 macrophages. These observations suggest that losartan inhibits LPS-induced proinflammatory gene expression in macrophages by activating the PPARgamma pathway rather than by the competitive inhibition of AT1R binding to AngII.

Abscisic acid synergizes with rosiglitazone to improve glucose tolerance and down-modulate macrophage accumulation in adipose tissue: Possible action of the cAMP/PKA/PPAR γ axis

Abscisic acid (ABA) is effective in preventing insulin resistance and obesity-related inflammation through a PPAR γ-dependent mechanism. The objective of this study was to assess the efficacy ABA in improving glucose homeostasis and suppress inflammation when administered in combination with rosiglitazone (Ros) and to determine whether PPAR γ activation by ABA is initiated via cAMP/protein kinase A (PKA) signaling. Obese db/db mice were fed high-fat diets containing 0, 10, or 70 mg/kg Ros with and without racemic ABA (100 mg/kg) for 60 days. Glucose tolerance and fasting insulin levels were assessed at 6 and 8 weeks, respectively, and adipose tissue macrophage (ATM) infiltration was examined by flow cytometry. Gene expression was examined on white adipose tissue (WAT) and stromal vascular cells (SVCs) cultured with ABA, Ros, or an ABA/Ros combination. Both Ros and ABA improved glucose tolerance, and ABA decreased plasma insulin levels while having no effect on Ros-induced weight gain. ABA in combination with low-dose Ros (10 mg/kg; Roslo) synergistically inhibited ATM infiltration. Treatment of SVCs with Ros, ABA or ABA/Ros suppressed expression of the M1 marker CCL17. ABA and Ros synergistically increased PPAR γ activity and pretreatment with a cAMP-inhibitor or a PKA-inhibitor abrogated ABA-induced PPAR γ activation. ABA and Ros act synergistically to modulate PPAR γ activity and macrophage accumulation in WAT and ABA enhances PPAR γ activity through a membrane-initiated mechanism dependent on cAMP/PKA signaling.

Conjugated Linoleic Acid Ameliorates Inflammation-Induced Colorectal Cancer in Mice through Activation of PPARγ1–3

Conjugated linoleic acid (CLA) exerts a protective effect on experimental inflammatory bowel disease and shows promise as a chemopreventive agent against colorectal cancer (CRC) in mice, although the mechanisms by which it exerts its beneficial effects against malignancies in the gut are not completely understood. Mice lacking PPARγ in immune and epithelial cells and PPARγ-expressing littermates were fed either control or CLA-supplemented (1 g CLA/100 g) diets to determine the role of PPARγ in inflammation-induced CRC. To induce tumor formation and colitis, mice were treated with azoxymethane and then challenged with 2% dextran sodium sulfate, respectively. Dietary CLA ameliorated disease activity, decreased colitis, and prevented adenocarcinoma formation in the PPARγ-expressing floxed mice but not in the tissue-specific PPARγ-null mice. Dietary CLA supplementation significantly decreased the percentages of macrophages in the mesenteric lymph nodes (MLN) regardless of the genotype and increased regulatory T cell numbers in MLN of PPARγ-expressing, but not in the tissue-specific, PPARγ-null mice. Colonic tumor necrosis factor-α mRNA expression was significantly suppressed in CLA-fed, PPARγ-expressing mice. This study suggests CLA ameliorates colitis and prevents tumor formation in part through a PPARγ-dependent mechanism.

WITHDRAWN: Down-regulation of collagen XVIII expression by thiazolidinediones through a PPARgamma-dependent mechanism in human non-small lung cancer cells.

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Duration of feeding linseed diet influences peroxisome proliferator-activated receptor γ and tumor necrosis factor gene expression, and muscle mass of growing–finishing barrows

The aim of the study was to investigate the effect of duration of feeding linseed (rich in n-3 PUFA) on peroxisome proliferator-activated receptor γ (PPARγ) and tumor necrosis factor (TNF-α) gene expression, and muscle mass of growing–finishing barrows. Two isoenergetic and isonitrogenous diets were formulated, and one of which was the basal diet and another one was the linseed diet including linseed at the level of 10%. Twenty-four Landrace × Yorkshire barrows weighing 35 ± 3.7 kg were randomly assigned to four treatments with six individuals per treatment. Pigs in treatment 1 (T1) fed the control diet throughout the experimental period, while pigs in T2, T3 and T4 fed the control diet except for 30, 60, and 90 d prior to slaughter when the linseed diet were fed. The experiment was conducted for 90 days. The longissimus muscle mass and each muscle mass in the hind leg were weighted. PPARγ and TNF-α mRNA expression levels in muscle, spleen and adipose tissue, and plasma concentrations of TNF-α data were measured and analyzed. The results showed that the longissimus muscle mass, quadriceps femoris muscle mass and semitendinosus muscle mass increased linearly ( P < 0.01) as prolonged the time of feeding linseed diet. The expression of PPARγ in longissimus muscle and spleen increased ( P < 0.01) linearly as prolonged the time of feeding linseed diet, while the expression of PPARγ in adipose tissue were not affected ( P = 0.095). Duration of linseed addition linearly decreased ( P < 0.01) TNF-α gene expression levels in the longissimus dorsi muscle, adipose and spleen, and serum concentration of TNF-α as well. The expression levels of PPARγ negatively correlated with the expression of TNF-α in muscle ( R 2 = 0.70, P < 0.001) and spleen ( R 2R 2 = 0.77, P < 0.001) respectively. Likewise, PPARγ expression level in spleen ( R 2R 2 = 0.59, P < 0.01) or muscle ( R 2R 2 = 0.52, P < 0.05) negative correlated with serum TNF-α concentration, while there were significant quadratic relation between muscular PPARγ ( R 2R 2 = 0.80, P < 0.01) or muscular TNF-α ( R 2R 2 = 0.87, P < 0.01) expression and the longissimus dorsi muscle mass. These data suggested that duration of feeding linseed diet lead to a linear decrease of TNF-α gene expression, which may increase the muscle mass in growing–finishing barrows, at least in part, through a PPARγ-dependent mechanism.

Peroxisome proliferator-activated receptor gamma agonist, rosiglitazone, suppresses CD40 expression and attenuates inflammatory responses after lithium pilocarpine-induced status epilepticus in rats

Inflammatory responses in the brain are involved in the etiopathogenesis and sequelae of seizures. Ligation of microglial CD40 plays a role in the development of inflammatory responses in the central nervous system (CNS). Our study showed that there was an increased CD40 expression on activated microglia in the brain injury after lithium pilocarpine-induced status epilepticus (SE) in rats. Since peroxisome proliferator-activated receptor gamma (PPARγ) acts as a regulator of CNS inflammation and a powerful pharmacological target for counteracting CNS diseases, we investigated the role of the PPARγ agonist, rosiglitazone, in the modulation of CD40 expression and in the pathological processes of inflammation after SE. We found that rosiglitazone inhibited the expression of CD40, tumor necrosis factor (TNF-α), and microglial activation in different regions of hippocampus. The results were indicated by immunohistochemistry, Western blot, and ELISA, respectively. Rosiglitazone also prevented neuronal loss in the CA1 area after SE observed by Nissl-staining. These protective effects were significantly reversed by the co-treatment with T0070907, a selective antagonist of the PPARγ, which clearly demonstrated a PPARγ-dependent mechanism. Our data provide evidence that rosiglitazone considerably attenuates inflammatory responses after SE by suppressing CD40 expression and microglial activation. Our data also support the idea that rosiglitazone might be a potential neuroprotective agent in epilepsy.

Arachidonic acid increases MCF‐10A and MCF‐10CA1 motility dependent on PPAR‐gamma

Recently, a high‐fat Western diet has been linked to an increase breast cancer risk. This high‐fat diet has an increased of omega‐6 (ω–6) poly‐unsaturated fatty acids (PUFAs) compared to omega‐3 (ω–3) PUFAs. We are investigating the role of one such ω‐6 PUFA, arachidonic acid (ArA), in breast cancer cell motility. ArA has been shown to be involved in increased cell motility and survival. Interestingly, ArA has also been shown to activate peroxisome‐proliferator activated receptor‐gamma (PPAR‐γ), a protein involved in adipocyte differentiation and plasminogen activator (PA) system regulation. We used two cell lines, MCF‐10CA1, an invasive carcinoma line and normal breast epithelial line, MCF‐10As, cells to study the effects of ArA. Chemotaxis to epidermal growth factor (EGF) was greatly increased in MCF‐10CA1 cells compared to the normal MCF‐10As. Arachidonic acid treatment increased chemotaxis in both cell lines about 2‐fold. Treatment with ArA increased uPA activity MCF‐10A cells, with a less dramatic increase in MCF‐10CA1 cells. To determine if ArA was acting on PPAR‐γ, we pretreated the cells with GW9662, a PPAR‐γ antagonist, and saw the ArA mediated increase in motility was abolished in both cell lines. This data suggests ArA increases cellular motility of normal and malignant cells through alterations in PA system components, through a PPAR‐γ dependent mechanism.

The trans-10, cis-12 isomer of conjugated linoleic acid decreases adiponectin assembly by PPARγ-dependent and PPARγ-independent mechanisms

The adipocyte-derived secretory protein adiponectin functions as an insulin-sensitizing agent. In plasma, adiponectin exists as low, medium, and high molecular weight oligomers. Treatment with trans-10, cis-12 conjugated linoleic acid (t-10, c-12 CLA) reduces levels of adiponectin as well as triglyceride (TG) in mice and adipocyte cell culture models. The aim of this study was to determine whether the effects of t-10, c-12 CLA on adiponectin and TG are mediated through modulation of the transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma). 3T3-L1 cells were treated either during or after differentiation into adipocytes with 100 microM t-10, c-12 CLA with or without 10 microM troglitazone, a PPARgamma agonist, or 1 microM GW9662, a PPARgamma antagonist, and adiponectin and TG levels were analyzed. Treatment with t-10, c-12 CLA reduced TG as well as cellular and secreted adiponectin levels and impaired the assembly of adiponectin oligomers. These changes were accompanied by decreases in PPARgamma mass. Troglitazone was able to reverse the t-10, c-12 CLA-mediated decrease in TG levels and restore the assembly of adiponectin oligomers but was unable to restore adiponectin synthesis. Conversely, treatment with GW9662 decreased TG mass and impaired adiponectin oligomer assembly but did not decrease total adiponectin mass. In a reporter assay, t-10, c-12 CLA appeared to be a partial PPARgamma agonist and prevented the stimulation of reporter activity by troglitazone. Therefore, the t-10, c-12 CLA isomer appears to alter adipocyte adiponectin metabolism through PPARgamma-dependent and PPARgamma-independent mechanisms.

PPARγ-dependent and -independent effects of Rosiglitazone on lipotoxic human pancreatic islets

We explored the in vitro effects of Rosiglitazone (RZG), a PPARγ agonist, on human pancreatic islet dysfunctions induced by chronic free fatty acid exposure. We demonstrated that RZG beneficial effects on insulin secretion and apoptosis did not imply PDX-1 or insulin gene modulation. It rather involved, through a PPARγ-dependent mechanism, a reduction of iNOS overexpressed in lipotoxic islets. This reduction likely led to the restoration of ATP level and insulin secretion as well as the decrease in apoptosis. More interestingly, we also demonstrated that RZG beneficial effects involved PPARγ-independent mechanisms. RZG treatment led to a limitation of oxidative stress exemplified by an increase of GPx and SOD expression. It also increased UCP2 expression that seemed to display antioxidant action in this model. Thus, RZG did not appear to exert a direct action on insulin expression but rather an indirect action on insulin secretion and apoptosis, through PPARγ-dependent and -independent mechanisms, via regulation of nitrogen and oxygen reactive species injury.

Inhibition of adhesive interaction between multiple myeloma and bone marrow stromal cells by PPARγ cross talk with NF-κB and C/EBPβ

Binding of multiple myeloma (MM) cells to bone marrow stromal cells (BMSCs) triggers expression of adhesive molecules and secretion of interleukin-6 (IL-6), promoting MM cell growth, survival, drug resistance, and migration, which highlights the possibility of developing and validating novel anti-MM therapeutic strategies targeting MM cells-host BMSC interactions and their sequelae. Recently, we have found that expression of the peroxisome proliferator-activated receptor gamma (PPARgamma) and its ligands can potently inhibit IL-6-regulated MM cell growth. Here we demonstrate that PPARgamma agonists 15-d-PGJ2 and troglitazone significantly suppress cell-cell adhesive events, including expression of adhesion molecules and IL-6 secretion from BMSCs triggered by adhesion of MM cells, as well as overcome drug resistance by a PPARgamma-dependent mechanism. The synthetic and natural PPARgamma agonists have diverging and overlapping mechanisms blocking transactivation of transcription factors NF-kappaB and 5'-CCAAT/enhancer-binding protein beta (C/EBPbeta). Both 15-d-PGJ2 and troglitazone blocked C/EBPbeta transcriptional activity by forming PPARgamma complexes with C/EBPbeta. 15-d-PGJ2 and troglitazone also blocked NF-kappaB activation by recruiting the coactivator PGC-1 from p65/p50 complexes. In addition, 15-d-PGJ2 had a non-PPARgamma-dependent effect by inactivation of phosphorylation of IKK and IkappaB. These studies provide the framework for PPARgamma-based pharmacological strategies targeting adhesive interactions of MM cells with the bone marrow microenvironment.

PGJ2 Inhibition of LPS-induced Inflammatory Mediator Expression from Rat Alveolar Macrophages

Studies suggested that 15-deoxy-Δ-12,14-prostaglandin J2 (PGJ2) may exert anti-inflammatory effects, including in the lung. Thus, in vitro studies were conducted to (1) investigate whether PGJ2 inhibited the production of inflammatory mediators from lipopolysaccharide (LPS)-exposed primary rat alveolar macrophages (AM), and (2) investigate possible mechanisms underlying PGJ2-mediated inhibition of inflammatory mediator production. These studies determined that PGJ2 inhibited LPS-induced nitric oxide (NO) production in a concentration- and time-dependent manner. PGJ2-mediated inhibition of NO, as well as of tumor necrosis factor-α (TNF-α) and macrophage inflammatory protein-2 (MIP-2), was also determined to be dependent on the time of addition of PGJ2 relative to LPS, and suggested the PGJ2 inhibitory mechanism is an early event. PGJ2 was shown not to interfere with binding or internalization of LPS by AM, indicating this was not responsible for PGJ2 inhibitory effects. Another possible mechanism underlying PGJ2-mediated inhibition was via peroxisome proliferator-activated receptor-γ (PPAR-γ). However, biochemical studies suggested that PGJ2-mediated inhibition was not occurring through PPAR-γ dependent mechanism, and molecular studies further established that both LPS and PGJ2 decrease PPAR-γ mRNA expression. A third possible mechanism underlying PGJ2-mediated inhibition was by alteration of nuclear factor (NF)-κB. Molecular studies confirmed that LPS stimulated NF-κB mRNA expression, and PGJ2 reduced this stimulation, which is consistent with PGJ2 effect on LPS-induced production of NO, TNF-α and MIP-2. Thus, data in this study established that PGJ2 inhibited LPS-induced inflammatory mediator production in rat AM, and this inhibition is mediated, at least in part, by reducing the expression of NF-κB mRNA.

Loss of PPARγ in immune cells impairs the ability of abscisic acid to improve insulin sensitivity by suppressing monocyte chemoattractant protein-1 expression and macrophage infiltration into white adipose tissue

Abscisic acid (ABA) is a natural phytohormone and peroxisome proliferator-activated receptor γ (PPARγ) agonist that significantly improves insulin sensitivity in db/db mice. Although it has become clear that obesity is associated with macrophage infiltration into white adipose tissue (WAT), the phenotype of adipose tissue macrophages (ATMs) and the mechanisms by which insulin-sensitizing compounds modulate their infiltration remain unknown. We used a loss-of-function approach to investigate whether ABA ameliorates insulin resistance through a mechanism dependent on immune cell PPARγ. We characterized two phenotypically distinct ATM subsets in db/db mice based on their surface expression of F4/80. F4/80 hi ATMs were more abundant and expressed greater concentrations of chemokine receptor (CCR) 2 and CCR5 when compared to F4/80 lo ATMs. ABA significantly decreased CCR2 + F4/80 hi infiltration into WAT and suppressed monocyte chemoattractant protein-1 (MCP-1) expression in WAT and plasma. Furthermore, the deficiency of PPARγ in immune cells, including macrophages, impaired the ability of ABA to suppress the infiltration of F4/80 hi ATMs into WAT, to repress WAT MCP-1 expression and to improve glucose tolerance. We provide molecular evidence in vivo demonstrating that ABA improves insulin sensitivity and obesity-related inflammation by inhibiting MCP-1 expression and F4/80 hi ATM infiltration through a PPARγ-dependent mechanism.