The role of peroxisome proliferator-activated receptors in pulmonary vascular disease

The pan-PPAR agonist lanifibranor reduces development of lung fibrosis and attenuates cardiorespiratory manifestations in a transgenic mouse model of systemic sclerosis

Background

The TβRII∆k-fib transgenic (TG) mouse model of scleroderma replicates key fibrotic and vasculopathic complications of systemic sclerosis through fibroblast-directed upregulation of TGFβ signalling. We have examined peroxisome proliferator-activated receptor (PPAR) pathway perturbation in this model and explored the impact of the pan-PPAR agonist lanifibranor on the cardiorespiratory phenotype.

Methods

PPAR pathway gene and protein expression differences from TG and WT sex-matched littermate mice were determined at baseline and following administration of one of two doses of lanifibranor (30 mg/kg or 100 mg/kg) or vehicle administered by daily oral gavage up to 4 weeks. The prevention of bleomycin-induced lung fibrosis and SU5416-induced pulmonary hypertension by lanifibranor was explored.

Results

Gene expression data were consistent with the downregulation of the PPAR pathway in the TβRII∆k-fib mouse model. TG mice treated with high-dose lanifibranor demonstrated significant protection from lung fibrosis after bleomycin and from right ventricular hypertrophy following induction of pulmonary hypertension by SU5416, despite no significant change in right ventricular systolic pressure.

Conclusions

In the TβRII∆k-fib mouse strain, treatment with 100 mg/kg lanifibranor reduces the development of lung fibrosis and right ventricular hypertrophy induced by bleomycin or SU5416, respectively. Reduced PPAR activity may contribute to the exaggerated fibroproliferative response to tissue injury in this transgenic model of scleroderma and its pulmonary complications.

Cardiovascular Effects Mediated by HMMR and CD44

Cardiovascular disease (CVD) is the leading cause of death worldwide. The most dangerous life-threatening symptoms of CVD are myocardial infarction and stroke. The causes of CVD are not entirely clear, and new therapeutic targets are still being sought. One of the factors involved in CVD development among vascular damage and oxidative stress is chronic inflammation. It is known that hyaluronic acid plays an important role in inflammation and is regulated by numerous stimuli, including proinflammatory cytokines. The main receptors for hyaluronic acid are CD44 and RHAMM. These receptors are membrane proteins that differ in structure, but it seems that they can perform similar or synergistic functions in many diseases. Both RHAMM and CD44 are involved in cell migration and wound healing. However, their close association with CVD is not fully understood. In this review, we describe the role of both receptors in CVD.

TGF-β1 attenuates mitochondrial bioenergetics in pulmonary arterial endothelial cells via the disruption of carnitine homeostasis

Transforming growth factor beta-1 (TGF-β1) signaling is increased and mitochondrial function is decreased in multiple models of pulmonary hypertension (PH) including lambs with increased pulmonary blood flow (PBF) and pressure (Shunt). However, the potential link between TGF-β1 and the loss of mitochondrial function has not been investigated and was the focus of our investigations. Our data indicate that exposure of pulmonary arterial endothelial cells (PAEC) to TGF-β1 disrupted mitochondrial function as determined by enhanced mitochondrial ROS generation, decreased mitochondrial membrane potential, and disrupted mitochondrial bioenergetics. These events resulted in a decrease in cellular ATP levels, decreased hsp90/eNOS interactions and attenuated shear-mediated NO release. TGF-β1 induced mitochondrial dysfunction was linked to a nitration-mediated activation of Akt1 and the subsequent mitochondrial translocation of endothelial NO synthase (eNOS) resulting in the nitration of carnitine acetyl transferase (CrAT) and the disruption of carnitine homeostasis. The increase in Akt1 nitration correlated with increased NADPH oxidase activity associated with increased levels of p47^phox, p67^phox, and Rac1. The increase in NADPH oxidase was associated with a decrease in peroxisome proliferator-activated receptor type gamma (PPARγ) and the PPARγ antagonist, GW9662, was able to mimic the disruptive effect of TGF-β1 on mitochondrial bioenergetics. Together, our studies reveal for the first time, that TGF-β1 can disrupt mitochondrial function through the disruption of cellular carnitine homeostasis and suggest that stimulating carinitine homeostasis may be an avenue to treat pulmonary vascular disease.

5-HT induces PPAR γ reduction and proliferation of pulmonary artery smooth muscle cells via modulating GSK-3β/β-catenin pathway

Studies have shown that peroxisome proliferator-activated receptor γ (PPAR γ) is down-regulated in pulmonary vascular lesions of patients with pulmonary hypertension (PH) and animal models of PH. Yet, the detailed molecular mechanisms underlying this alteration are not fully defined; the aim of this study is to address this issue. 5-HT dose- and time-dependently reduced PPAR γ expression and promoted pulmonary artery smooth muscle cells (PASMCs) proliferation; this was accompanied with the phosphorylation of Akt, inactivation of GSK-3β and up-regulation of β-catenin. Importantly, pre-treatment of cells with PI3K inhibitor (Ly294002) or prior silencing of β-catenin with siRNA blocked 5-HT-induced PPAR γ reduction and PASMCs proliferation. In addition, inactivation or lack of GSK-3β or inhibition of proteasome function up-regulated β-catenin protein without affecting its mRNA level and reduced PPAR γ protein expression. Taken together, our study indicates that 5-HT suppresses PPAR γ expression and stimulates PASMCs proliferation by modulating GSK-3β/β-catenin axis, and suggests that targeting this pathway might have potential value in the management of PH.

Pan-PPAR agonist IVA337 is effective in experimental lung fibrosis and pulmonary hypertension

Objective

To evaluate the antifibrotic effects of the pan-peroxisome proliferator-activated receptor (PPAR) agonist IVA337 in preclinical mouse models of pulmonary fibrosis and related pulmonary hypertension (PH).

Methods

IVA337 has been evaluated in the mouse model of bleomycin-induced pulmonary fibrosis and in Fra-2 transgenic mice, this latter being characterised by non-specific interstitial pneumonia and severe vascular remodelling of pulmonary arteries leading to PH. Mice received two doses of IVA337 (30 mg/kg or 100 mg/kg) or vehicle administered by daily oral gavage up to 4 weeks.

Results

IVA337 demonstrated at a dose of 100 mg/kg a marked protection from the development of lung fibrosis in both mouse models compared with mice receiving 30 mg/kg of IVA337 or vehicle. Histological score was markedly reduced by 61% in the bleomycin model and by 50% in Fra-2 transgenic mice, and total lung hydroxyproline concentrations decreased by 28% and 48%, respectively, as compared with vehicle-treated mice. IVA337 at 100 mg/kg also significantly decreased levels of fibrogenic markers in lesional lungs of both mouse models. In addition, IVA337 substantially alleviated PH in Fra-2 transgenic mice by improving haemodynamic measurements and vascular remodelling. In primary human lung fibroblasts, IVA337 inhibited in a dose-dependent manner fibroblast to myofibroblasts transition induced by TGF-β and fibroblast proliferation mediated by PDGF.

Conclusion

We demonstrate that treatment with 100 mg/kg IVA337 prevents lung fibrosis in two complementary animal models and substantially attenuates PH in the Fra-2 mouse model. These findings confirm that the pan-PPAR agonist IVA337 is an appealing therapeutic candidate for these cardiopulmonary involvements.

The mechanistic basis of prostacyclin and its stable analogues in pulmonary arterial hypertension: Role of membrane versus nuclear receptors

Pulmonary arterial hypertension (PAH) is a progressive disease of distal pulmonary arteries in which patients suffer from elevated pulmonary arterial pressure, extensive vascular remodelling and right ventricular failure. To date prostacyclin (PGI2) therapy remains the most efficacious treatment for PAH and is the only approved monotherapy to have a positive impact on long-term survival. A key thing to note is that improvement exceeds that predicted from vasodilator testing strongly suggesting that additional mechanisms contribute to the therapeutic benefit of prostacyclins in PAH. Given these agents have potent antiproliferative, anti-inflammatory and endothelial regenerating properties suggests therapeutic benefit might result from a slowing, stabilization or even some reversal of vascular remodelling in vivo. This review discusses evidence that the pharmacology of each prostacyclin (IP) receptor agonist so far developed is distinct, with non-IP receptor targets clearly contributing to the therapeutic and side effect profile of PGI2 (EP3), iloprost (EP1), treprostinil (EP2, DP1) along with a family of nuclear receptors known as peroxisome proliferator-activated receptors (PPARs), to which PGI2 and some analogues directly bind. These targets are functionally expressed to varying degrees in arteries, veins, platelets, fibroblasts and inflammatory cells and are likely to be involved in the biological actions of prostacylins. Recently, a highly selective IP agonist, selexipag has been developed for PAH. This agent should prove useful in distinguishing IP from other prostanoid receptors or PPAR binding effects in human tissue. It remains to be determined whether selectivity for the IP receptor gives rise to a superior or inferior clinical benefit in PAH.

MicroRNA-27b plays a role in pulmonary arterial hypertension by modulating peroxisome proliferator-activated receptor γ dependent Hsp90-eNOS signaling and nitric oxide production

Pulmonary artery endothelial dysfunction is associated with pulmonary arterial hypertension (PAH). Based on recent studies showing that microRNA (miR)-27b is aberrantly expressed in PAH, we hypothesized that miR-27b may contribute to pulmonary endothelial dysfunction and vascular remodeling in PAH. The effect of miR-27b on pulmonary endothelial dysfunction and the underlying mechanism were investigated in human pulmonary artery endothelial cells (HPAECs) in vitro and in a monocrotaline (MCT)-induced model of PAH in vivo. miR-27b expression was upregulated in MCT-induced PAH and inversely correlated with the levels of peroxisome proliferator-activated receptor (PPAR)-γ, and miR-27b inhibition attenuated MCT-induced endothelial dysfunction and remodeling and prevented PAH associated right ventricular hypertrophy and systolic pressure in rats. PPARγ was confirmed as a direct target of miR-27b in HPAECs and shown to mediate the effect of miR-27b on the disruption of endothelial nitric oxide synthase (eNOS) coupling to Hsp90 and the suppression of NO production associated with the PAH phenotype. We showed that miR-27b plays a role endothelial function and NO release and elucidated a potential mechanism by which miR-27b regulates Hsp90-eNOS and NO signaling by modulating PPARγ expression, providing potential therapeutic targets for the treatment of PAH.

Rosiglitazone preserves pulmonary vascular function in lambs with increased pulmonary blood flow

BACKGROUND

Pulmonary vascular function is impaired with increased pulmonary blood flow (PBF). We hypothesized that a peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist would mitigate this effect.

METHODS

An aorta-to-pulmonary-artery shunt was placed in 11 fetal lambs. Lambs received the PPAR-γ agonist rosiglitazone (RG, 3 mg/kg/d, n = 6) or vehicle (n = 5) for 4 wk. Lung tissue from five normal 4-wk-old lambs was used for comparisons.

RESULTS

At 4 wk, pulmonary artery pressure (PAP) and vascular resistance (PVR) decreased with inhaled nitric oxide (NO) in RG- and vehicle-treated shunt lambs. PAP and PVR decreased with acetylcholine (Ach) in RG-treated, but not vehicle-treated, shunt lambs. In vehicle-treated shunt lambs, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, rac1, superoxide, and 3-nitrotyrosine (3-NT) levels were increased, and Ser1177 endothelial NO synthase (eNOS) protein was decreased as compared with normal lambs. In RG-treated shunt lambs, NOx, Ser1177 eNOS protein, and eNOS activity were increased, and NADPH activity, rac1, superoxide levels, and 3-NT levels were decreased, as compared with vehicle-treated shunt lambs. PPAR-γ protein expression was lower in vehicle-treated shunt lambs than in normal and RG-treated shunt lambs.

CONCLUSION

The PPAR-γ agonist RG prevents the loss of agonist-induced endothelium-dependent pulmonary vascular relaxation in lambs with increased PBF, in part, due to decreased oxidative stress and/or increased NO production.

Chronic inhibition of PPAR-γ signaling induces endothelial dysfunction in the juvenile lamb

We have recently shown that the development of endothelial dysfunction in lambs with increased pulmonary blood flow (PBF) correlates with a decrease in peroxisome proliferator activated receptor-γ (PPAR-γ) signaling. Thus, in this study we determined if the loss of PPAR-γ signaling is necessary and sufficient to induce endothelial dysfunction by exposing lambs with normal PBF to the PPAR-γ antagonist, GW9662. Two-weeks of exposure to GW9662 significantly decreased both PPAR-γ protein and activity. In addition, although eNOS protein and nitric oxide metabolites (NO(x)) were significantly increased, endothelial dependent pulmonary vasodilation in response to acetylcholine was attenuated, indicative of endothelial dysfunction. To elucidate whether downstream mediators of vasodilation were impaired we examined soluble guanylate cyclase (sGC)-α and β subunit protein, cGMP levels, and phosphodiesterase 5 (PDE5) protein and activity, but we found no significant changes. However, we found that peroxynitrite levels were significantly increased in GW9662-treated lambs and this correlated with a significant increase in protein kinase G-1α (PKG-1α) nitration and a reduction in PKG activity. Peroxynitrite is formed by the interaction of NO with superoxide and we found that there was a significant increase in superoxide generation in GW9662-treated lambs. Further, we identified dysfunctional mitochondria as the primary source of the increased superoxide. Finally, we found that the mitochondrial dysfunction was due to a disruption in carnitine metabolism. We conclude that loss of PPAR-γ signaling is sufficient to induce endothelial dysfunction confirming its important role in maintaining a healthy vasculature.

PPAR-γ regulates carnitine homeostasis and mitochondrial function in a lamb model of increased pulmonary blood flow

Objective

Carnitine homeostasis is disrupted in lambs with endothelial dysfunction secondary to increased pulmonary blood flow (Shunt). Our recent studies have also indicated that the disruption in carnitine homeostasis correlates with a decrease in PPAR-γ expression in Shunt lambs. Thus, this study was carried out to determine if there is a causal link between loss of PPAR-γ signaling and carnitine dysfunction, and whether the PPAR-γ agonist, rosiglitazone preserves carnitine homeostasis in Shunt lambs.

Methods and Results

siRNA-mediated PPAR-γ knockdown significantly reduced carnitine palmitoyltransferases 1 and 2 (CPT1 and 2) and carnitine acetyltransferase (CrAT) protein levels. This decrease in carnitine regulatory proteins resulted in a disruption in carnitine homeostasis and induced mitochondrial dysfunction, as determined by a reduction in cellular ATP levels. In turn, the decrease in cellular ATP attenuated NO signaling through a reduction in eNOS/Hsp90 interactions and enhanced eNOS uncoupling. In vivo, rosiglitazone treatment preserved carnitine homeostasis and attenuated the development of mitochondrial dysfunction in Shunt lambs maintaining ATP levels. This in turn preserved eNOS/Hsp90 interactions and NO signaling.

Conclusion

Our study indicates that PPAR-γ signaling plays an important role in maintaining mitochondrial function through the regulation of carnitine homeostasis both in vitro and in vivo. Further, it identifies a new mechanism by which PPAR-γ regulates NO signaling through Hsp90. Thus, PPAR-γ agonists may have therapeutic potential in preventing the endothelial dysfunction in children with increased pulmonary blood flow.

PPARγ as a Potential Target to Treat Airway Mucus Hypersecretion in Chronic Airway Inflammatory Diseases

Airway mucus hypersecretion (AMH) is a key pathophysiological feature of chronic airway inflammatory diseases such as bronchial asthma, cystic fibrosis, and chronic obstructive pulmonary disease. AMH contributes to the pathogenesis of chronic airway inflammatory diseases, and it is associated with reduced lung function and high rates of hospitalization and mortality. It has been suggested that AMH should be a target in the treatment of chronic airway inflammatory diseases. Recent evidence suggests that a key regulator of airway inflammation, hyperresponsiveness, and remodeling is peroxisome proliferator-activated receptor gamma (PPARγ), a ligand-activated transcription factor that regulates adipocyte differentiation and lipid metabolism. PPARγ is expressed in structural, immune, and inflammatory cells in the lung. PPARγ is involved in mucin production, and PPARγ agonists can inhibit mucin synthesis both in vitro and in vivo. These findings suggest that PPARγ is a novel target in the treatment of AMH and that further work on this transcription factor may lead to new therapies for chronic airway inflammatory diseases.

Peroxisome Proliferator-Activated Receptor-gamma Ligands: Potential Pharmacological Agents for Targeting the Angiogenesis Signaling Cascade in Cancer

Peroxisome proliferator-activated receptor-γ (PPAR-γ) has currently been considered as molecular target for the treatment of human metabolic disorders. Experimental data from in vitro cultures, animal models, and clinical trials have shown that PPAR-γ ligand activation regulates differentiation and induces cell growth arrest and apoptosis in a variety of cancer types. Tumor angiogenesis constitutes a multifaceted process implicated in complex downstream signaling pathways that triggers tumor growth, invasion, and metastasis. In this aspect, accumulating in vitro and in vivo studies have provided extensive evidence that PPAR-γ ligands can function as modulators of the angiogenic signaling cascade. In the current review, the crucial role of PPAR-γ ligands and the underlying mechanisms participating in tumor angiogenesis are summarized. Targeting PPAR-γ may prove to be a potential therapeutic strategy in combined treatments with conventional chemotherapy; however, special attention should be taken as there is also substantial evidence to support that PPAR-γ ligands can enhance angiogenic phenotype in tumoral cells.

New perspectives for the treatment of pulmonary hypertension

Pulmonary hypertension (PH) is a debilitating disease with a poor prognosis. Therapeutic options remain limited despite the introduction of prostacyclin analogues, endothelin receptor antagonists and phosphodiesterase 5 inhibitors within the last 15 years; these interventions address predominantly the endothelial and vascular dysfunctionS associated with the condition, but simply delay progression of the disease rather than offer a cure. In an attempt to improve efficacy, emerging approaches have focused on targeting the pro-proliferative phenotype that underpins the pulmonary vascular remodelling in the lung and contributes to the impaired circulation and right heart failure. Many novel targets have been investigated and validated in animal models of PH, including modulation of guanylate cyclases, phosphodiesterases, tyrosine kinases, Rho kinase, bone morphogenetic proteins signalling, 5-HT, peroxisome proliferator activator receptors and ion channels. In addition, there is hope that combinations of such treatments, harnessing and optimizing vasodilator and anti-proliferative properties, will provide a further, possibly synergistic, increase in efficacy; therapies directed at the right heart may also offer an additional benefit. This overview highlights current therapeutic options, promising new therapies, and provides the rationale for a combination approach to treat the disease.

HO-1 Induced by Cilostazol Protects Against TNF-α-associated Cytotoxicity via a PPAR-γ-dependent Pathway in Human Endothelial Cells

A large body of evidence has indicated that induction of endogenous antioxidative proteins seems to be a reasonable strategy for delaying the progression of cell injury. In our previous study, cilostazol was found to increase the expression of the antioxidant enzyme heme oxygenase-1 (HO-1) in synovial cells. Thus, the present study was undertaken to examine whether cilostazol is able to counteract tumor necrosis factor-α (TNF-α)-induced cell death in endothelial cells via the induction of HO-1 expression. We exposed human umbilical vein endothelial cells (HUVECs) to TNF-α (50 ng/ml), with or without cilostazol (10 µM). Pretreatment with cilostazol markedly reduced TNF-α-induced viability loss in the HUVECs, which was reversed by zinc protoporphyrine IX (ZnPP), an inhibitor of HO-1. Moreover, cilostazol increased HO-1 protein and mRNA expression. Cilostazol-induced HO-1 induction was markedly attenuated not only by ZnPP but also by copper-protoporphyrin IX (CuPP). In an assay measuring peroxisome proliferator-activated receptor-γ (PPAR-γ) transcription activity, cilostazol directly increased PPAR-γ transcriptional activity which was completely abolished by HO-1 inhibitor. Furthermore, increased PPAR-γ activity by cilostazol and rosiglitazone was completely abolished in cells transfected with HO-1 siRNA. Taken together, these results indicate that cilostazol up-regulates HO-1 and protects cells against TNF-α-induced endothelial cytotoxicity via a PPAR-γ-dependent pathway.

IUGR decreases PPARγ and SETD8 Expression in neonatal rat lung and these effects are ameliorated by maternal DHA supplementation

Intrauterine growth restriction (IUGR) is associated with altered lung development in human and rat. The transcription factor PPARγ, is thought to contribute to lung development. PPARγ is activated by docosahexanoic acid (DHA). One contribution of PPARγ to lung development may be its direct regulation of chromatin modifying enzymes, such as Setd8. In this study, we hypothesized that IUGR would result in a gender-specific reduction in PPARγ, Setd8 and associated H4K20Me levels in the neonatal rat lung. Because DHA activates PPARγ, we also hypothesized that maternal DHA supplementation would normalize PPARγ, Setd8, and H4K20Me levels in the IUGR rat lung. We found that IUGR decreased PPARγ levels, with an associated decrease in Setd8 levels in both male and female rat lungs. Levels of the Setd8-dependent histone modification, H4K20Me, were reduced on the PPARγ gene in both males and females while whole lung H4K20Me was only reduced in male lung. Maternal DHA supplementation ameliorated these effects in offspring. We conclude that IUGR decreases lung PPARγ, Setd8 and PPARγ H4K20Me independent of gender, while decreasing whole lung H4K20Me in males only. These outcomes are offset by maternal DHA. We speculate that maintenance of the epigenetic milieu may be one role of PPARγ in the lung and suggests a novel benefit of maternal DHA supplementation in IUGR.

Heme oxygenase-1/p21WAF1 mediates peroxisome proliferator-activated receptor-gamma signaling inhibition of proliferation of rat pulmonary artery smooth muscle cells

Activation of peroxisome proliferator-activated receptor (PPAR)-gamma suppresses proliferation of rat pulmonary artery smooth muscle cells (PASMCs), and therefore ameliorates the development of pulmonary hypertension in animal models. However, the molecular mechanisms underlying this effect remain largely unknown. This study addressed this issue. The PPARgamma agonist rosiglitazone dose-dependently stimulated heme oxygenase (HO)-1 expression in PASMCs, 5 microm rosiglitazone inducing a 12.1-fold increase in the HO-1 protein level. Cells pre-exposed to rosiglitazone showed a dose-dependent reduction in proliferation in response to serotonin; this was abolished by pretransfection of cells with sequence-specific small interfering RNA against HO-1. In addition, rosiglitazone stimulated p21(WAF1) expression in PASMCs, a 2.34-fold increase in the p21(WAF1) protein level being achieved with 5 microm rosiglitazone; again, this effect was blocked by knockdown of HO-1. Like loss of HO-1, loss of p21(WAF1) through siRNA transfection also reversed the inhibitory effect of rosiglitazone on PASMC proliferation triggered by serotonin. Taken together, our findings suggest that activation of PPARgamma induces HO-1 expression, and that this in turn stimulates p21(WAF1) expression to suppress PASMC proliferation. Our study also indicates that rosiglitazone, a medicine widely used in the treatment of type 2 diabetes mellitus, has potential benefits for patients with pulmonary hypertension.

Effect of PPARgamma inhibition on pulmonary endothelial cell gene expression: gene profiling in pulmonary hypertension

Peroxisome proliferator-activated receptor type gamma (PPARgamma) is a subgroup of the PPAR transcription factor family. Recent studies indicate that loss of PPARgamma is associated with the development of pulmonary hypertension (PH). We hypothesized that the endothelial dysfunction associated with PPARgamma inhibition may play an important role in the disease process by altering cellular gene expression and signaling cascades. We utilized microarray analysis to determine if PPARgamma inhibition induced changes in gene expression in pulmonary arterial endothelial cells (PAEC). We identified 100 genes and expressed sequence tags (ESTs) that were upregulated by >1.5-fold and 21 genes and ESTs that were downregulated by >1.3-fold (P < 0.05) by PPARgamma inhibition. The upregulated genes can be broadly classified into four functional groups: cell cycle, angiogenesis, ubiquitin system, and zinc finger proteins. The genes with the highest fold change in expression: hyaluronan-mediated motility receptor (HMMR), VEGF receptor 2 (Flk-1), endothelial PAS domain protein 1 (EPAS1), basic fibroblast growth factor (FGF-2), and caveolin-1 in PAEC were validated by real time RT-PCR. We further validated the upregulation of HMMR, Flk-1, FGF2, and caveolin-1 by Western blot analysis. In keeping with the microarray results, PPARgamma inhibition led to re-entry of cell cycle at G(1)/S phase and cyclin C upregulation. PPARgamma inhibition also exacerbated VEGF-induced endothelial barrier disruption. Finally we confirmed the downregulation of PPARgamma and the upregulation of HMMR, Flk-1, FGF2, and Cav-1 proteins in the peripheral lung tissues of an ovine model of PH. In conclusion, we have identified an array of endothelial genes modulated by attenuated PPARgamma signaling that may play important roles in the development of PH.

Effect of PPARgamma inhibition on pulmonary endothelial cell gene expression: gene profiling in pulmonary hypertension

Peroxisome proliferator-activated receptor type gamma (PPARgamma) is a subgroup of the PPAR transcription factor family. Recent studies indicate that loss of PPARgamma is associated with the development of pulmonary hypertension (PH). We hypothesized that the endothelial dysfunction associated with PPARgamma inhibition may play an important role in the disease process by altering cellular gene expression and signaling cascades. We utilized microarray analysis to determine if PPARgamma inhibition induced changes in gene expression in pulmonary arterial endothelial cells (PAEC). We identified 100 genes and expressed sequence tags (ESTs) that were upregulated by >1.5-fold and 21 genes and ESTs that were downregulated by >1.3-fold (P < 0.05) by PPARgamma inhibition. The upregulated genes can be broadly classified into four functional groups: cell cycle, angiogenesis, ubiquitin system, and zinc finger proteins. The genes with the highest fold change in expression: hyaluronan-mediated motility receptor (HMMR), VEGF receptor 2 (Flk-1), endothelial PAS domain protein 1 (EPAS1), basic fibroblast growth factor (FGF-2), and caveolin-1 in PAEC were validated by real time RT-PCR. We further validated the upregulation of HMMR, Flk-1, FGF2, and caveolin-1 by Western blot analysis. In keeping with the microarray results, PPARgamma inhibition led to re-entry of cell cycle at G(1)/S phase and cyclin C upregulation. PPARgamma inhibition also exacerbated VEGF-induced endothelial barrier disruption. Finally we confirmed the downregulation of PPARgamma and the upregulation of HMMR, Flk-1, FGF2, and Cav-1 proteins in the peripheral lung tissues of an ovine model of PH. In conclusion, we have identified an array of endothelial genes modulated by attenuated PPARgamma signaling that may play important roles in the development of PH.

PPAR-gamma signaling pathway in placental development and function: a potential therapeutic target in the treatment of gestational diseases

BACKGROUND

PPAR-gamma is a target for the treatment of metabolic disorders, as Pioglitazone and Rosiglitazone are already used against type 2 diabetes. Pleiotropic functions, such as antiproliferative and anti-inflammatory effects against several pathological states, including cardiovascular disease and cancer, are currently being explored in clinical studies.

OBJECTIVE

Evidence indicates that PPAR-gamma is expressed in the placenta, playing a crucial role in placental development and function, while PPAR-gamma ligands appear to modulate fetal membrane signals. Thus, in the last few years, the pivotal role of PPAR-gamma in placental biology has been the focus of extensive research, as diabetes appears to be the most common metabolic dysfunction in pregnancy.

METHODS

We aim to present data concerning the expression of PPAR-gamma in animal and human placenta, underlining its significance in normal placental development and several gestational diseases. The effects of PPAR-gamma ligands as modulators of placental biology in normal and certain pathological conditions are also discussed.

RESULTS/CONCLUSION

Current research provides substantial evidence that PPAR-gamma plays a pivotal role in placental biology and may reveal new perspectives in the treatment of gestational diseases.