Peroxisome proliferator-activated receptor gamma1 expression in porcine white blood cells: dynamic regulation with acute endotoxemia

Association of a genetic variant in the angiopoietin-like protein 4 gene with metabolic syndrome

Background

Metabolic syndrome (MetS) is characterized by a clustering of cardiovascular risk factors that include: abdominal obesity, dyslipidemia, hypertension and glucose intolerance. Angiopoietin-like protein 4 (ANGPTL4) is a circulating peptide that is an inhibitor of lipoprotein lipase, a key enzyme in lipid metabolism. The objective of this study was to investigate the association of ANGPTL4 gene variants (E40K) with fasting serum triglyceride levels and with cardiovascular risk factors, that included the presence of MetS in 817 subjects recruited from the Mashhad stroke and heart Atherosclerosis Disorders (MASHAD) cohort Study.

Method

ANGPTL4 genotypes were determined using a TaqMan genotyping based real time PCR method. The association of the genetic variant with the risk of metabolic syndrome and its relationship with lipid profile were determined.

Result

The frequency of GG, GA and AA genotypes were 96.9, 2.7 and 0.4% in individuals with MetS, and 78.8, 20.8, 0.4%, in those without MetS. The GA genotype of the rs116843064 polymorphism was associated with a lower risk for MetS (e.g., OR in Codominant genetic model: 0.14, 95% CI: (0.06–0.33), p < 0.0001). Subject with an A allele had a higher risk for MetS (OR: 6.72, 95% CI: (3.05–14.82), p < 0.0001). There was a significant difference in fasted lipid profiles across the genotypes for ANGPTL4. Carriers of the AG genotype had higher levels of serum HDL-cholesterol (HDL-C) and lower TG, compared to the GG homozygotes genotype.

Conclusion

The G allele at the rs116843064 polymorphic locus of the ANGPTL4 gene was associated with a lower prevalence of MetS.

Oyster crude polysaccharides attenuates lipopolysaccharide-induced cytokines production and PPARγ expression in weanling piglets

This study evaluated whether oyster crude polysaccharides (OPS) attenuates lipopolysaccharide (LPS)-induced immune stress in weanling piglets. Thirty healthy crossbred piglets (28 ± 1 days old) were randomly divided into five groups (6 piglets/group). Blank control and LPS groups were fed with the basal diet, while low, medium and high dose of OPS groups were fed with the basal diet supplemented with 0.5, 0.8 and 1.2 % OPS, respectively, for 30 days. LPS group, as well as low, medium and high dose of OPS groups were then injected intraperitoneally with LPS (100 μg/kg body weight), whereas the blank control group was given phosphate buffered saline. The concentrations of TNF-α, IL-1β and IL-6 in plasma were detected by ELISA. The mRNA levels of PPARγ in liver, spleen, adrenal gland and thymus were evaluated by quantitative real-time PCR. The results showed that compared with the blank control, LPS treatment significantly increased plasma IL-1β, IL-6 and TNF-α levels, which was significantly attenuated by supplementing 0.5, 0.8 or 1.2 % OPS in the diet. In addition, LPS significantly induced expression of PPARγ mRNA in liver, spleen, adrenal gland, and thymus, which was blocked by adding OPS regardless of the doses. These results indicate that dietary supplementation of OPS was able to alleviate the immune stress induced by LPS.

Phosphorylation of extracellular signal-regulated kinase (ERK)-1/2 Is associated with the downregulation of peroxisome proliferator-activated receptor (PPAR)-γ during polymicrobial sepsis

Peroxisome proliferator-activated receptor (PPAR)-γ is a ligand-activated transcription factor and regulates inflammation. Posttranslational modifications regulate the function of PPARγ, potentially affecting inflammation. PPARγ contains a mitogen-activated protein kinase (MAPK) site, and phosphorylation by extracellular signal-regulated kinase (ERK)-1/2 leads to inhibition of PPARγ. This study investigated the kinetics of PPARγ expression and activation in parenchymal and immune cells in sepsis using the MAPK/ERK kinase (MEK)-1 inhibitor, an upstream kinase of ERK1/2. Adult male Sprague Dawley rats were subjected to polymicrobial sepsis by cecal ligation and puncture. Rats received intraperitoneal injection of vehicle or the MEK1 inhibitor PD98059 (5 mg/kg) 30 min before cecal ligation and puncture. Rats were euthanized at 0, 1, 3, 6 and 18 h after cecal ligation and puncture. Control animals used were animals at time 0 h. Lung, plasma and peripheral blood mononuclear cells (PBMCs) were collected for biochemical assays. In vehicle-treated rats, polymicrobial sepsis resulted in significant lung injury. In the lung and PBMCs, nuclear levels of PPARγ were decreased and associated with an increase in phosphorylated PPARγ and phosphorylated ERK1/2 levels. Treatment with the MEK1 inhibitor increased the antiinflammatory plasma adipokine adiponectin, restored PPARγ expression in PBMCs and lung, and decreased lung injury. The inflammatory effects of sepsis cause changes in PPARγ expression and activation, in part, because of phosphorylation of PPARγ by ERK1/2. This phosphorylation can be reversed by ERK1/2 inhibition, thereby improving lung injury.

Anti‐inflammatory Effect of PPARγ in Cultured Human Mesangial Cells

Our aim is to investigate whether peroxisome proliferator-activator receptor-gamma (PPARgamma) expression was altered in human mesangial cells under inflammatory stress and whether PPARgamma could retard the inflammatory responses. Based on cultured human mesangial cell lines (HMCLs), PPARgamma expressions at protein and mRNA levels were observed by Western blot analysis and reverse transcriptase polymerase chain reaction. Informatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) were measured by enzyme-linked immunosorbent assay. Our results demonstrated that PPARgamma protein expression was dramatically increased in HMCLs stimulated by IL-1beta (10 ng/mL). The levels of IL-6 and TNF-alpha in HMCL supernatants, protein, and mRNA expressions of PPARgamma in IL-1beta challenge cells were significantly increased more than those in untreated cells. Importantly, PPARgamma agonists troglitazone, rosiglitazone, and 15-deoxy-delta(12, 14)-prosglandin J2 significantly decreased the up expression of TNF-alpha and IL-6 in HMCL supernatants stimulated by IL-1beta. Furthermore, troglitazone downregulated TNF-alpha and IL-6 mRNA expression from IL-1beta challenge HMCLs. Our data suggest that PPARgamma plays an important role in mesangial cells responding to inflammatory stress. PPARgamma may prove to be a pharmacological target in glomerulonephritis.

Up-regulated expression of peroxisome proliferator-activated receptor gamma in the hypothalamic-pituitary-adrenal axis of weaned pigs after Escherichia coli lipopolysaccharide challenge

The expression of peroxisome proliferator-activated receptor gamma (PPARgamma) was investigated in the hypothalamic-pituitary-adrenal (HPA) axis of weaned pigs after injection with 100 microg/kg bodyweight Escherichia coli lipopolysaccharide (LPS) (n=6) and control pigs injected with sterile saline (n=6). LPS increased PPARgamma mRNA and protein expression in the hypothalamus (23.8 and 3.1-fold relative to controls, respectively), pituitary gland (9.2 and 2.0-fold, respectively) and adrenal gland (3.5 and 2.3-fold, respectively) (P<0.05). LPS also induced an increase in PPARgamma immunohistochemical staining in the hypothalamus (1.3-fold), adenohypophysis (1.3-fold), adrenal cortex (1.4-fold) and adrenal medulla (1.6-fold) (P<0.05). Concurrent with up-regulated expression of PPARgamma, LPS increased the concentrations of plasma corticotrophin-releasing hormone (2.1-fold) and adrenocorticotrophin (1.4-fold) (P<0.05). LPS also induced elevations of interleukin 6 and tumour necrosis factor alpha mRNA levels in the hypothalamus (4.0 and 3.2-fold, respectively), pituitary gland (20.7 and 5.1-fold, respectively) and adrenal gland (3.9 and 3.3-fold, respectively) (P<0.05). PPARgamma may play a role in the regulation of neuroendocrine responses associated with immunological stress in pigs.

Thiazolidinediones and the preservation of beta-cell function, cellular proliferation and apoptosis

The thiazolidinediones (TZDs) or glitazones are pharmaceutical agents that have profound effects on energy expenditure and conservation. They also exert significant anti-inflammatory effects and influence cell proliferation and cell death. The drugs are primarily used in clinical practice in the treatment of patients with type 2 diabetes mellitus, a disorder of insulin resistance that occurs when the pancreatic beta-cells are unable to produce adequate amounts of insulin to maintain euglycaemia. Loss of pancreatic beta-cell function in type 2 diabetes is progressive and often precedes overt diabetes by 10 years or more, as was shown by the United Kingdom Prospective Diabetes Study. Any therapeutic or preventive approach that would limit or reverse loss of beta-cell function in diabetes would have profound effects on the morbidity associated with this widespread disease. Evidence suggesting a potential role of TZDs in preserving beta-cell function in type 2 diabetes as well as the ability of these agents to exert anti-inflammatory and proapoptotic anticancer effects, and their ability to promote cellular proliferation in various organs is reviewed.

Sepsis-induced inhibition of neutrophil chemotaxis is mediated by activation of peroxisome proliferator-activated receptor-{gamma}

Neutrophils (polymorphonuclear leukocytes [PMNs]) are critical to the immune response, including clearance of infectious pathogens. Sepsis is associated with impaired PMN function, including chemotaxis. PMNs express peroxisome proliferator-activated receptor-gamma (PPAR-gamma), a ligand-activated nuclear transcription factor involved in immune and inflammatory regulation. The role of PPAR-gamma in PMN responses, however, is not well characterized. We report that freshly isolated human PMNs constitutively express PPAR-gamma, which is up-regulated by the sepsis-induced cytokines TNF-alpha and IL-4. PMN chemotactic responses to formylmethionyl-leucyl-phenylalanine (fMLP) and IL-8 were dose-dependently inhibited by treatment with the PPAR-gamma ligands troglitazone and 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) and by transfection of PMN-like HL-60 cells with a constitutively active PPAR-gamma construct. Inhibition of chemotaxis by PPAR-gamma ligands correlated with decreases in extracellular signal-regulated kinase-1 and -2 activation, actin polymerization, and adherence to a fibrinogen substrate. Furthermore, PMN expression of PPAR-gamma was increased in sepsis patients and mice with either of 2 models of sepsis. Finally, treatment with the PPAR-gamma antagonist GW9662 significantly reversed the inhibition of PMN chemotaxis and increased peritoneal PMN recruitment in murine sepsis. This study indicates that PPAR-gamma activation is involved in PMN chemotactic responses in vitro and may play a role in the migration of these cells in vivo.

The effect of Chlamydia pneumoniae on the expression of peroxisome proliferator-activated receptor-gamma in vascular smooth muscle cells

PURPOSE

This study was designed to investigate the change of peroxisome proliferator-activated receptor gamma (PPARgamma) after the infection of the human coronary artery smooth muscle cells (HCSMCs) with Chlamydia pneumoniae (C. pneumoniae) and the effect of PPARgamma agonist on the expression of PPARgamma of C. pneumoniae-infected HCSMCs.

MATERIALS AND METHODS

To determine the effect of PPARgamma agonist on the proliferation of C. pneumoniae-infected HCSMCs, rosiglitazone at various concentrations was applied 1 hour before inoculation of HCSMCs.

RESULTS

The expression of PPARgamma mRNA in HCSMCs increased from 3 hours after C. pneumoniae infection and reached that of noninfected HCSMCs at 24 hours (p<0.05). The expression of PPARgamma protein in HCSMCs also increased from 3 hours after C. pneumoniae and persisted until 24 hours as compared with that of noninfected HCSMCs (p<0.05). The pretreatment of HCSMCs with rosiglitazone followed by the infection with C. pneumoniae augmented the expression of PPARgamma mRNA and protein (p<0.05) and decreased cell proliferation.

CONCLUSION

Our results showed that the expression of PPARgamma increases in response to C. pneumoniae infection and rosiglitazone further augmented the expression of PPARgamma. It is suggested that rosiglitazone could ameliorate the chronic inflammation in the vessel wall induced by C. pneumoniae by augmenting PPARgamma expression.

Increased expression of the peroxisome proliferator-activated receptor gamma in the immune system of weaned pigs after Escherichia coli lipopolysaccharide injection

Peroxisome proliferator-activated receptor gamma (PPARgamma), a member of the nuclear hormone receptor superfamily, has been implicated in regulation of immunity and inflammation in rodents and humans. The objective of the current study was to investigate whether the expression of PPARgamma was altered in the immune system of weaned pigs after Escherichia coli lipopolysaccharide (LPS) injection. PPARgamma expression was investigated in the thymus, spleen, mesenteric lymph node and peripheral white blood cells of weaned pigs (8.54+/-0.24 kg BW) after LPS injection (100 microg/kg BW, n=6) and controls (sterile saline, n=6), by using real-time polymerase chain reaction, Western blot analysis, and immunohistochemistry. Plasma pro-inflammatory cytokines and hormones were also assessed. LPS triggered PPARgamma mRNA and protein expression in the thymus (P<0.05, 4.24-fold; P<0.10, 1.46-fold), spleen (P<0.10, 2.75-fold; P<0.05, 1.84-fold), mesenteric lymph node (P<0.05, 4.32-fold; P<0.05, 1.96-fold) and peripheral white blood cells (P<0.001, 24.44-fold; P<0.001, 1.58-fold). The LPS-injected pigs showed an increase in PPARgamma staining in splenic corpuscle and periarterial lymphatic sheath of white pulp (P<0.05) and red pulp (P<0.001) of spleen, and in medullas of thymus lobule of thymus (P<0.05), and in thymus-dependent area of mesenteric lymph node (P<0.05) compared to the control pigs. Concurrent with up-regulation of PPARgamma expression, LPS induced increases in plasma interleukin-6 (P<0.001), tumor necrosis factor-alpha (P<0.001), cortisol (P<0.001), prostaglandin E(2) (P<0.01) and 15-deoxy-Delta(12,14)-prostaglandin J(2) (15 d-PGJ(2)) (P<0.05), and decreases in plasma insulin (P<0.10) and insulin-like growth factor-1 (P<0.001). These results suggest that induction of PPARgamma expression in immune system may be associated with the release of the natural PPARgamma activating ligand 15 d-PGJ(2), and play an important role in host response to immunological stress. Additionally, it is possible that PPARgamma would be a new therapeutic target in treatment of immunological stress of livestock.

Anti-inflammatory effects of PPAR-gamma agonists directly correlate with PPAR-gamma expression during acute pancreatitis

Peroxisome proliferator-activated receptors (PPARs) are ligand-inducible transcription factors that regulate cellular energy and lipid metabolism. PPAR-gamma agonists also have potent anti-inflammatory properties through down-regulation of early inflammatory response genes. The role of PPAR-gamma in acute pancreatitis has not been adequately examined. In this study, we determined the effect of PPAR-gamma agonists on the severity of pancreatitis and sought to correlate PPAR-gamma expression in pancreatic acinar cells and the severity of acute pancreatitis in vivo. Acute pancreatitis was induced in mice by hyperstimulation with the cholecystokinin analog, cerulein. PPAR-gamma agonists were administered by intraperitoneal injection 15-30 minutes before induction of pancreatitis (pretreatment) or at various times after induction of pancreatitis (treatment). Pancreata and serum were harvested over the course of 24 hours. Serum amylase activity and glucose levels were measured. Pancreata were used for histological evaluation as well as protein and mRNA analysis. Pretreatment of mice with the PPAR-gamma agonists 15-deoxy-Delta12, 14-prostaglandin J(2), or troglitazone significantly reduced the severity of pancreatitis in a dose-dependent manner. This reduction was indicated by reduced serum amylase activity and histological damage (leukocyte infiltration, vacuolization, and necrosis). Although cerulein decreased PPAR-gamma expression in the pancreas, pretreatment with agonists maintained PPAR-gamma expression early in acute pancreatitis. The expression of PPAR-gamma inversely correlated with pancreatitis severity and expression of the proinflammatory cytokines, interleukin-6, and tumor necrosis factor-alpha. Treatment with troglitazone after the induction of pancreatitis reduced serum amylase activity. The results suggest that PPAR-gamma plays a direct role in the inflammatory cascade during the early events of acute pancreatitis. Our data are the first to demonstrate that PPAR-gamma agonists represent a promising therapeutic strategy for acute pancreatitis.

Peroxisome proliferator-activated receptor-gamma antagonists GW9662 and T0070907 reduce the protective effects of lipopolysaccharide preconditioning against organ failure caused by endotoxemia

OBJECTIVE

There is evidence that a) ligands of the nuclear receptor peroxisome proliferator-activated receptor (PPAR)-gamma and b) lipopolysaccharide preconditioning protect the organs against the multiple organ injury and dysfunction caused by endotoxemia. Here we investigate the hypothesis that the protective effects of lipopolysaccharide preconditioning are due to an enhanced formation of endogenous ligands of PPAR-gamma.

DESIGN

Prospective, randomized study.

SETTING

University-based research laboratory.

SUBJECTS

Ninety-nine anesthetized male Wistar rats.

INTERVENTIONS

Rats were pretreated with low-dose lipopolysaccharide (1 mg/kg intraperitoneally, 24 hrs before induction of endotoxemia) in the absence or presence of the selective PPAR-gamma antagonists GW9662 (1 mg/kg intraperitoneally) or T0070907 (1 mg/kg intraperitoneally) or the selective cyclooxygenase-2 inhibitor parecoxib (20 mg/kg intraperitoneally). At 24 hrs after preconditioning with low-dose lipopolysaccharide, the rats were subjected to acute severe endotoxemia (lipopolysaccharide 6 mg/kg intravenously).

MEASUREMENTS AND MAIN RESULTS

Lipopolysaccharide preconditioning significantly attenuated the development of renal dysfunction (serum creatinine), hepatocellular injury (serum alanine aminotransferase and aspartate aminotransferase), and circulatory failure (hypotension) as well as the increase in the plasma levels of interleukin-1beta caused by severe endotoxemia. All of these beneficial effects afforded by preconditioning with lipopolysaccharide were attenuated by the specific PPAR-gamma antagonists used. In contrast, the cyclooxygenase-2 inhibitor parecoxib did not affect the beneficial effects afforded by preconditioning with lipopolysaccharide.

CONCLUSIONS

We propose that endogenous ligands of PPAR-gamma contribute to the protection afforded by lipopolysaccharide preconditioning against the organ injury and dysfunction associated with severe endotoxemia in the rat.

Peroxisome proliferator-activated receptor-gamma is a new therapeutic target in sepsis and inflammation

Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a member of the nuclear receptor superfamily and a ligand-activated transcription factor with pleiotropic effects on lipid metabolism, inflammation, and cell proliferation. PPARgamma forms a heterodimer with the retinoid X receptor and upon ligand-activation binds to the PPAR response element in the promoter of genes to allow transcription. The class of insulin-sensitizing drugs known as thiazolidinediones have been identified as specific PPARgamma agonists that have allowed the characterization of many genes regulated by PPARgamma. Thiazolidinediones include rosiglitazone, pioglitazone, troglitazone, and ciglitazone. In addition to these synthetic agonists, cyclopentenone prostaglandins of the J2 series have been identified as natural ligands for PPARgamma. Several in vitro and in vivo studies have demonstrated that pharmacological activation of PPARgamma by 15-deoxy-Delta(12,14)-PGJ2 (15d-PGJ2) or thiazolidinediones has anti-inflammatory effects. This article provides an overview of the role of PPARgamma in regulating the inflammatory response and emphasizes the potential efficacy of PPARgamma ligands as novel therapeutic approaches beyond diabetes in sepsis, inflammation, and reperfusion injury.

The selective PPARγ antagonist GW9662 reverses the protection of LPS in a model of renal ischemia-reperfusion

BACKGROUND

We have recently reported that pretreatment of rats with endotoxin (lipopolysaccharide, LPS) and selective agonists of the nuclear receptor peroxisome proliferator-activated receptor-gamma (PPARgamma) protect the kidney against ischemia/reperfusion (I/R) injury. Here we investigate the hypothesis that the renoprotective effects of LPS may be due to an enhanced formation of endogenous ligands of PPARgamma, rather than an up-regulation of PPARgamma expression.

METHODS

Rats were pretreated with LPS (1 mg/kg, IP, 24 hours prior to ischemia) in the absence (control) or presence of the selective PPARgamma antagonist GW9662 (1 mg/kg, IP, 24 and 12 hours prior to ischemia). Twenty-four hours after injection of LPS, rats were subjected to 60 minutes of bilateral renal ischemia, followed by 6 hours of reperfusion. Serum and urinary indicators of renal injury and dysfunction were measured, specifically serum creatinine, aspartate aminotransferase, and gamma-glutamyl-transferase, creatinine clearance, urine flow, and fractional excretion of sodium. Kidney PPARgamma1 mRNA levels were determined by reverse transcriptase-polymerase chain reaction.

RESULTS

Pretreatment with LPS significantly attenuated all markers of renal injury and dysfunction caused by I/R. Most notably, GW9662 abolished the protective effects of LPS. Additionally, I/R caused an up-regulation of kidney PPARgamma1 mRNA levels compared to sham animals, which were unchanged in rats pretreated with LPS.

CONCLUSION

We document here for the first time that endogenous ligands of PPARgamma may contribute to the protection against renal I/R injury afforded by LPS pretreatment in the rat.

Peroxisome Proliferator Activator Receptor-γ Ligands, 15-Deoxy-Δ12,14-Prostaglandin J2 and Ciglitazone, Reduce Systemic Inflammation in Polymicrobial Sepsis by Modulation of Signal Transduction Pathways

Peroxisome proliferator activator receptor-gamma (PPARgamma) is a nuclear receptor that controls the expression of several genes involved in metabolic homeostasis. We investigated the role of PPARgamma during the inflammatory response in sepsis by the use of the PPARgamma ligands, 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) and ciglitazone. Polymicrobial sepsis was induced by cecal ligation and puncture in rats and was associated with hypotension, multiple organ failure, and 50% mortality. PPARgamma expression was markedly reduced in lung and thoracic aorta after sepsis. Immunohistochemistry showed positive staining for nitrotyrosine and poly(ADP-ribose) synthetase in thoracic aortas. Plasma levels of TNF-alpha, IL-6, and IL-10 were increased. Elevated activity of myeloperoxidase was found in lung, colon, and liver, indicating a massive infiltration of neutrophils. These events were preceded by degradation of inhibitor kappaBalpha (IkappaBalpha), activation of IkappaB kinase complex, and c-Jun NH(2)-terminal kinase and, subsequently, activation of NF-kappaB and AP-1 in the lung. In vivo treatment with ciglitazone or 15d-PGJ(2) ameliorated hypotension and survival, blunted cytokine production, and reduced neutrophil infiltration in lung, colon, and liver. These beneficial effects of the PPARgamma ligands were associated with the reduction of IkappaB kinase complex and c-Jun NH(2)-terminal kinase activation and the reduction of NF-kappaB and AP-1 DNA binding in the lung. Furthermore, treatment with ciglitazone or 15d-PGJ(2) up-regulated the expression of PPARgamma in lung and thoracic aorta and abolished nitrotyrosine formation and poly(ADP-ribose) expression in aorta. Our data suggest that PPARgamma ligands attenuate the inflammatory response in sepsis through regulation of the NF-kappaB and AP-1 pathways.

Sepsis-induced immunosuppression: from bad to worse

The sepsis syndrome is characterized by the acute release of a variety of inflammatory mediators, which often result in detrimental effects to the host. The release of these mediators is regulated and counterbalanced by the coordinated expression of antiinflammatory molecules. It is the balance between the expression of pro- and antiinflammatory mediators that often determines the magnitude of early tissue injury and subsequent risk of infectious complications. As our understanding of the pathophysiology of sepsis continues to evolve, we have gained a greater appreciation for the effects that sepsis and similar states of overwhelming stress have on host antimicrobial immunity. A number of functional defects in leukocytes isolated from sepsis patients have been characterized. These defects include diminished expression of important cell surface antigens, dysregulated cytokine production, alterations in antigen-presenting ability, and accelerated apoptosis. Impaired leukocyte function has important clinical ramifications, as high mortality rates have been observed in patients displaying evidence of sepsis-induced immune deactivation. In this article, we review the current literature supporting evidence of dysregulation of host immunity occurring during sepsis syndrome, characterize the underlying pathophysiology, and describe novel therapeutic interventions directed at augmenting host immunity during sepsis.

Cyclooxygenase-2 is induced in monocytes by peroxisome proliferator activated receptor gamma and oxidized alkyl phospholipids from oxidized low density lipoprotein

Low density lipoprotein (LDL) oxidation and monocyte infiltration of the vessel wall underlie atherogenesis. These cells express cyclooxygenase-2, but the way oxidized LDL stimulates cyclooxygenase-2 transcription is unknown. Oxidized LDL, oxidatively fragmented phospholipids isolated from oxidized LDL, a synthetic oxidized alkylphospholipid (azPC) that is a potent peroxisome proliferator activated receptor (PPAR) gamma agonist, or the PPARgamma agonist rosiglitazone all induced cyclooxygenase-2 expression and enhanced prostaglandin E(2) (PGE(2)) secretion in primary human monocytes. The cyclooxygenase-2 inhibitor NS398 blocked PPARgamma-induced PGE(2) secretion. Phospholipase A(1) and A(2) digestion shows that oxidized alkylphospholipids, and not oxidized fatty acids, were the relevant agonists. The upstream PPAR-responsive element (PPRE) of cyclooxygenase-2 was required for induction of a luciferase reporter by oxidized phospholipids, azPC, and rosiglitazone, and a (COX-2 PPRE)(3)-luciferase reporter was responsive to these PPARgamma agonists. Circulating human monocytes do not contain PPARgamma, but PPARgamma was induced rapidly (<4 h) in monocytes upon ligation of surface ICAM-3, but not P-selectin glycoprotein-1 even though both interactions prime cytokine secretion. Cyclooxygenase-2 induction by oxidized phospholipids only occurred in monocytes containing PPARgamma. Thus PPARgamma was induced rapidly in primary monocytes by appropriate outside-in signaling, sensitizing them to previously undetectable agonists in oxidized LDL. Cyclooxygenase-2 and PGE(2) secretion are induced, not inhibited, by selective PPARgamma agonists that include oxidatively fragmented phospholipids in oxidized LDL.

Peroxisome proliferator-activated receptor gamma (PPARgamma) and its ligands: a review

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of a class of nuclear hormone receptors intimately involved in the regulation of expression of myriad genes that regulate energy metabolism, cell differentiation, apoptosis and inflammation. Although originally discovered as a pivotal regulator of adipocyte differentiation, the roles that this transcription factor play in physiology and pathophysiology continue to grow as researchers discover its influence in the function of many cell types. This review highlights the roles that PPARgamma play in the regulation of gene expression associated with normal cell physiology as well as the pathophysiology of multiple diseases including obesity, diabetes and cancer. Additionally, naturally occurring and pharmaceutical ligands for the receptor as well as the potential role of PPARgamma as the receptor responsible for fatty acid-induced effects on gene expression will be described.

Delayed activation of PPARgamma by LPS and IFN-gamma attenuates the oxidative burst in macrophages

Desensitization of macrophages is important during the development of sepsis. It was our intention to identify mechanisms that promote macrophage deactivation upon contact with endotoxin (LPS) and interferon-gamma (IFN-gamma) in vitro. Macrophage activation was achieved with 12-O-tetradecanoylphorbol 13-acetate (TPA), and the oxidative burst (i.e., oxygen radical formation) was followed by oxidation of the redox-sensitive dyes hydroethidine and dichlorodihydrofluorescein diacetate. Prestimulation of macrophages for 15 h with a combination of LPS/IFN-gamma attenuated oxygen radical formation in response to TPA. Taking the anti-inflammatory properties of the peroxisome proliferator-activating receptorgamma (PPARgamma) into consideration, we established activation of PPARgamma in response to LPS/IFN-gamma by an electrophoretic mobility shift, supershift, and a reporter gene assay. The reporter contains a triple PPAR-responsive element (PPRE) in front of a thymidine kinase minimal promoter driving the luciferase gene. We demonstrated that PPRE decoy oligonucleotides, supplied in front of LPS/IFN-gamma, allowed a full oxidative burst to recover upon TPA addition. Furthermore, we suppressed the oxidative burst by using the PPARgamma agonists 15-deoxy-Delta12,14-prostaglandin J2, BRL 49653, or ciglitazone. No effect was observed with WY 14643, a PPARalpha agonist. We conclude that activation of PPARs, most likely PPARgamma, promotes macrophage desensitization, thus attenuating the oxidative burst. This process appears important during development of sepsis.